Air Conditioner Compressor Failure

Air Conditioner Compressor Failure

How To Diagnose an a/c Compressor Failure and Prevent It From Happening Again

Adapted from an article written by Larry Carley for Import Car magazine

The compressor is the heart of the refrigeration circuit. It pumps and pressurizes the refrigerant to move it through the A/C system. Compressors work hard and run hot, up to several hundred degrees and several hundred pounds per square inch of internal pressure. They rely on only a few ounces of lubricant to keep their parts moving. If the lubricant is lost because of a leak, or the lubricant breaks down due to contamination, the compressor will not last. Sooner or later, the compressor will call it quits.

The most common symptom of a compressor failure (besides no cooling) is a seized compressor. It will not turn when the magnetic clutch engages, and you may hear squeals of protest from the drive belt. Or, the belt may have already broken or been thrown off its pulleys.

Loss of lubrication is unquestionably the most common cause of compressor failure. This can happen when there is a refrigerant leak somewhere in the system that allows refrigerant and oil to escape. Typical leak points are hoses, hose and pipe connections (O-rings and flange gaskets), the evaporator, condenser or the compressor shaft seal. An electronic leak detector or dye should be used to find the leak so it can be repaired.

A restriction inside the A/C system can also starve the compressor for oil. Oil circulates with the refrigerant, so if the orifice tube or expansion valve is blocked it may cause the compressor to run dry and seize.

Even if a compressor is still turning, it may have to be replaced if it is leaking, making excessive noise or not working correctly. Some compressors are naturally noisier than others, but loud knocking noises can sometimes be caused by air in the system (the cure here is to vacuum purge the system to remove the unwanted air, then to recharge the system with refrigerant). Metallic noises and bearing noise are usually signals that the compressor is about to fail.

A new compressor may be needed if the unit is leaking internally or not producing enough pressure due to bad reed valves, worn piston rings, or worn or scored cylinders, etc.). A worn compressor or one with internal problems will not be able to develop normal operating pressures with a full charge of refrigerant. This kind of problem can be diagnosed with an A/C gauge set.

Poor cooling can also be caused by a lot of things other than a bad compressor, so do not replace the compressor until you have ruled out other possibilities such as a low refrigerant charge, too much oil in the system, air contamination, a clogged condenser, plugged orifice tube, inoperative electric cooling fan, etc.

Compressor operation can be affected by sensors in vehicles with automatic temperature control systems. Some have an A/C pressure transducer (usually mounted in the high side line) to monitor refrigerant pressure and shut off the compressor if pressure gets too high; a compressor temperature sensor to turn off the compressor if it gets too hot; and/or a compressor rpm sensor to monitor belt slippage. Mitsubishi, for example, uses a "belt lock controller" to disengage the compressor if the drive belt slips or the compressor seizes.

On 1996 and newer Mercedes-Benz E-Class cars, the A/C control module will disengage the compressor if the refrigerant temperature and pressure sensors do not show a rise when the compressor is being driven.

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COMPRESSOR CLUTCH PROBLEMSIf the compressor is not turning, make sure the magnetic clutch engages when energized. Underlying problems here may include a bad relay, fuse, wiring problem or a defective clutch. If the clutch fails to cycle on and off when the A/C is turned on, jumping the clutch lead with a jumper wire from the battery will show if the problem is in the clutch or elsewhere. If the clutch engages, the problem is the clutch power supply (relay, fuse, wiring, switch or control module). Refer to a wiring diagram and work backward toward the battery to find out why the voltage is not getting through.

Many A/C systems have a low-pressure cutout switch that prevents the compressor clutch from engaging if system pressure (the refrigerant charge) is too low. This is designed to protect the compressor from damage in the event of a leak. So if the clutch is not engaging, check the refrigerant charge and the cutout switch. The clutch air gap is also important for proper clutch operation. If the clearance is not correct, the clutch may slip and burn or not engage at all. The specs can be found in a service manual along with adjustment procedures. Generally speaking, most clutches call for a 0.015 to 0.040 inch press fit clearance.

DEFECTIVE COMPRESSORS?How often do compressors fail as a result of "manufacturing defects?" Not very often. According to one compressor manufacturer who examined 75 compressors that had failed and were returned under warranty, only two were found to have manufacturing defects. The rest failed because of problems such as too little oil in the system, air in the system, contaminants in the system, or "installer error." The latter category included using the wrong type of compressor lubricant, not using enough lubricant, using non-approved flushes to "clean" system parts, and using cross-contaminated refrigerants. Debris left over from a previous compressor failure was the most common cause of repeat compressor failures.

Always use the type of lubricant recommended for specific compressors. This is especially important with rotary vane and scroll-type compressors. A replacement compressor may or may not contain lubricant from the factory. In some cases, the shipping oil must be drained before the compressor is installed. In other cases, the compressor may contain a POE or a PAG oil lubricant that may or may not be compatible with the vehicle requirements. Follow the compressor suppliers installation instructions to the letter to avoid warranty problems later on.

Before adding fresh oil to a system, all the old oil should first be removed. This will prevent cross-contamination of lubricants and reduce the risk of overcharging the system with too much oil (which can cause cooling problems). Always refer to the OEM oil capacity chart for the vehicle application. The following is a list of recommended lubricants for R-134a import compressors:

• Behr/Bosch rotary compressors - Ester 100;
• Behr/Bosch piston compressors - PAG 46;
• Calsonic V5 - PAG 150;
• Calsonic V6 - PAG 46;
• Diesel/Kiki (Zexel) DKS, DKV & DCW - PAG 46;
• Hitachi (all) - PAG 46;
• Keihin (all) - PAG 46;
• Matsushita (all) - Ester 100;
• Mitsubishi FX80 - PAG 100;
• Mitsubishi FX105 - PAG 46;
• Nihon (all) - Ester 100;
• Nippondenso 6P, 10P, 10PA, 10P08E - PAG 46;
• Nippondenso SP127, SP134 & 6E171 - PAG 46;
• Nippondenso TV series - PAG 125;
• Panasonic (all) - PAG 46;
• Sanden SD500 & SD700 - PAG 100;
• Sanden SD710, SDB, TV & TRS - PAG 46; and
• Seik-Seiki (all) - Ester 100.

FLUSHING AFTER A COMPRESSOR FAILUREWhen a compressor fails, it may spit metallic debris into the A/C system. Most of this debris ends up in the condenser where it can block tubes and interfere with efficient cooling. Some of the debris may be carried to the orifice tube or expansion valve and create a blockage. Debris can even be blown back into the suction tube. If not removed by flushing, it can be sucked back into a new compressor and cause it to fail.

Flushing the hoses is always recommended following a compressor failure. Flushing the condenser is also recommended. But with many condensers, replacement is the only sure-fire way to get rid of contaminants. Older serpentine-style tube-and-fin condensers can often be flushed successfully, but parallel flow condensers are very difficult to clean. So too are newer style condensers with extremely small extruded tubes. For these kinds of applications, the condenser should be replaced. It is expensive, but not as expensive as ruining a new compressor because of residual debris or sludge in the old condenser.

After flushing, install an in-line filter after the condenser to trap any debris that might still be inside. The filter will prevent anything that works loose from being carried to the orifice tube.

You should also install a filter screen in the suction hose at the compressor inlet to protect the new compressor from any debris that might be upstream inside the suction hose or evaporator.

Another reason for flushing is to remove residual oil from the system. This is necessary when retrofitting an older R-12 system to the new ozone-safe R-134a refrigerant, but it is also a good way to make sure the system contains the right amount of oil. Simply adding oil to the system to replace that which has been lost is a guess at best, because there is no way to know how much has been lost due to leakage. Estimating a couple of ounces here and there for replacing an accumulator, receiver/drier, condenser, compressor or hoses is not a very accurate means of determining how much oil needs to be added to the system when it is recharged with refrigerant. Flushing gets rid of all the oil so the exact amount specified by the vehicle manufacturer can be added back to the system.

What happens if there is too little or too much compressor oil in the system? Not enough oil in the system will reduce compressor lubrication and may lead to premature failure. Too much oil in the system can puddle in the condenser and obstruct the flow of refrigerant causing a drop in cooling performance.

Other parts that should also be replaced following a compressor failure include the accumulator or receiver/dryer, and the orifice tube or expansion valve. The former contains a bag of desiccant that traps moisture and acts as a filter to protect the system. A new orifice tube or expansion valve is recommended because the small hole in this metering device can become easily plugged with debris. An aftermarket "variable orifice tube" can improve low-speed cooling.

EVACUATING & RECHARGING THE AIR CONDITIONING SYSTEMAfter the compressor has been installed and the hoses are reconnected, the A/C system must be thoroughly evacuated with a vacuum pump to pull out air and moisture. If not purged from the system, air will reduce cooling efficiency. Moisture will react with refrigerant oil and produce acids and sludge. Moisture can also freeze and plug the expansion valve causing noise, restrictions or a complete blockage.

A pump capable of achieving high vacuum must be used to pull out all of the contaminants. When air is pulled out of the system, it creates a vacuum that causes residual moisture to boil and evaporate. For this to occur, the vacuum pump must be capable of pulling at least 29 in. Hg of vacuum throughout the evacuation process (which normally takes about 30 minutes).

One of the best ways to monitor the evacuation process is with a Thermistor Vacuum Gauge that reads in microns (one inch of Mercury equals 25,400 microns). It takes a highly accurate instrument to measure vacuum because even a little pressure left in the system can prevent all the residual moisture from boiling out. Only a 1/2 inch of mercury of pressure (12,700 microns) can reduce the boiling point of water by more than 20 degrees F. Pulling out the last fraction of an inch of pressure is the most critical step in the evacuation process to ensure complete removal of all air and moisture.

After pulling a deep vacuum on an A/C system, close all valves and shut off the vacuum pump. A slow rise in pressure (which you can see on the Thermistor Vacuum Gauge) will occur as the residual moisture continues to boil off inside the system. Pulling additional vacuum will get rid of this moisture. The evacuation will not be complete until the system can maintain a stable vacuum reading below 700 microns for at least three minutes.

The time it takes to completely evacuate an A/C system can be reduced by preconditioning the evaporator prior to hooking up the vacuum pump. Preconditioning raises the temperature so the moisture will boil off faster. The easiest way to raise the temperature of the evaporator is to run the engine with the heater on HOT in the RECIRC mode. Turn the blower fan to HI and close all doors and windows. When the engine reaches normal operating temperature, the evaporator will be thoroughly preheated and ready to evacuate.

If you have difficulty maintaining a stable deep vacuum, there may be a leak in the A/C system, the vacuum pump or the equipment connections. Leak testing should be done prior to evacuating the system because evacuation is not always a reliable way to locate or even identify a small leak in an A/C system. Seals and O-rings that leak under pressure may move under evacuation and not leak.

Finally, recharge the system with the recommended amount of refrigerant and compressor oil. Do not overcharge and do not add too much oil. Check cooling performance to verify that everything is working properly and that the new compressor is doing its job.

GM Analysis of Compressor Failures A recently completed analysis of air conditioning compressors in General Motors vehicles that had been replaced for noise, vibration and insufficient cooling concerns has indicated a high number of no trouble found results. Further studies have shown that the root cause of the customer concerns that might lead to a compressor replacement was often a state of refrigerant charge issue or in another area or system of the vehicle. The A/C system refrigerant charge level, either high or low, has been found to be a major contributor to unnecessary compressor replacement. The ability of a refrigerant recycling/recharging tool to recover and measure the weight of the A/C system refrigerant charge will help the technician make a more accurate diagnosis of a charge level concern prior to any component replacement. A thorough visual inspection should always be performed before any tests or repairs are done. Doing so may find an obvious problem that will save time and eliminate the need for extensive diagnosis. Some additional items, as listed below, should be considered before a compressor is replaced for noise, vibration or insufficient cooling concerns. The compressor mounting bolts, brackets or braces may be loose or missing. The compressor drive belt may be frayed, loose or misaligned. The A/C refrigerant lines may be grounding out on body, chassis or engine components. This may allow noise and vibration to be transmitted into the passenger compartment. The air flow through the condenser may be insufficient. The condenser fins may be bent or filled with debris, or the space between the condenser and radiator may be filled with leaves or debris, or the cooling fans may be inoperative or not performing as designed, or the installation of aftermarket accessories may alter or restrict the air flow through the condenser. Inspect for missing or mispositioned air deflectors, baffles, seals and shrouds. The compressor cycling switch may not be operating correctly. This may allow the evaporator core to freeze up or the compressor may not stay engaged long enough for proper system pressures to develop. The air flow through the evaporator core may be restricted. The cabin filter may be plugged, or the evaporator core may be covered with debris, or the cowl air inlet leaf screen may by plugged. The A/C system may be overcharged or undercharged with refrigerant. The A/C system charge weight can be measured with the RRR tool after a refrigerant recovery is done. The A/C system may have an improper amount or incorrect type of refrigerant oil. An A/C system sealer is not approved for use in GM vehicles. The refrigerant may be contaminated or contain an excessive amount of air. The A/C system may have been charged with an unapproved refrigerant. The refrigerant identifier on the ACR 2000 should alert the technician to these conditions. The orifice tube or thermostatic expansion valve (TXV) may be restricted, plugged or inoperative. The capillary bulb on the TXV must be properly positioned so that the valve will provide proper refrigerant flow. The desiccant bag in the accumulator may have failed, allowing debris to circulate in the A/C system. The A/C system charge weight may have been changed. Components with an updated design may have been released. A check for service bulletins applicable to the vehicle being worked on should always be done. A check for diagnostic trouble codes in all the control modules on the vehicle should be done. Some trouble codes will disable compressor operation after they have set. They must be repaired and cleared before compressor operation is allowed. Verify that the engine is not operating with a low unstable idle, and that the engine is operating within the compressor engagement parameters (for example, the engine may be overheating or it may be too cold for compressor engagement). The diagnostic procedures in the HVAC section of the service manual should be performed as written to prevent the misdiagnosis of a customer concern. The HVAC Diagnostic System Check and the A/C System Performance Test are written for a specific model only. They are not generic charts. They follow a logical order with detailed instructions on how to perform each step. When a thorough HVAC system diagnosis indicates that the compressor should be replaced, follow the procedure in the appropriate service manual. The oil balance instructions are an important part of the replacement procedure. The correct refrigerant oil, as listed in the service manual, must be used in the new compressor. It is recommended that a suction screen filter be installed on Delphi Harrison compressors that do not already have one. The suction screen filter is not approved for use on compressors from other manufacturers. Refer to Corporate Bulletin Number 01-01-39-003A for more information on A/C suction screen kit repair recommendations and procedures. If the compressor has had a catastrophic internal failure, an inline filter may be required to capture the large amount of debris that may be found to be circulating in the A/C system. In addition, the A/C system may require flushing. Refer to Corporate Bulletin Number 01-01-38-006B for more information on flushing procedures and recommendations. The addition of fluorescent refrigerant leak dye to the A/C system is recommended if the vehicle does not have it installed already. Some vehicles have leak dye installed at the assembly plant and this will be indicated on the A/C charge label. Refer to Corporate Bulletin Number 00-01-38-009B for more information. If leak dye has been added during a previous repair and has been in the vehicle for more than three years, it is recommended that additional dye be added. Finally, a leak check of the entire A/C system should be performed before the vehicle goes back on the road. Courtesy of General Motors. More Air Conditioning Articles: Flushing Air Conditioning Compressors Compressor PAG Oil Applications Air Conditioning Inspection Checklist How to Recharge Your Air Conditioning System How to Troubleshoot Your Air Conditioning System Air Conditioning No Cooling MACS Recommended A/C Service Procedures Air Conditioning Service Best Practices (Procedures a repair shop should follow when servicing your A/C system) Retrofitting Older R-12 A/C Systems to R-134a Troubleshoot Automatic Climate Control System A/C Service Equipment: What's Required To Service Today's Vehicles The New A/C Refrigerants  Click Here To See More Carley Automotive Technical Articles R134a A/C Retrofit Guide covers refrigerant conversions

Troubleshoot Automatic Climate Control System

Troubleshoot Automatic Climate Control System

Today's automatic climate control systems allow hands-free temperature regulator, whether hot or cold. Once you set a temperature on your car's automatic climate control system, it should maintain that temperature regardless of what's going on outside.

HOW AUTOMATIC CLIMATE CONTROL DIFFERS FROM MANUAL AIR CONDITIONING

Manual air conditioning systems are just what the name implies: they require he A/C temperature settings to be adjusted manually. Manual A/C systems have an on-off switch, a temperature control knob or slide switch and a knob or switch for adjusting fan speed.

With a manual A/C system, you turn on the A/C when you want cool air and select a temperature setting and blower speed. If the air gets too cold, you turn down the blower speed or change the position of the temperature setting. If the air isn't cold enough, you crank it all the way up.

The temperature slide switch on most manual systems is connected with cables or vacuum hoses to the airflow control doors inside the HVAC (heating ventilation air conditioning) unit under the instrument panel. Changing the temperature setting opens or closes the doors to increase or decrease airflow through the A/C evaporator. It is a relatively simple, trouble-free control system that does not require a lot of complicated electronics.

Automatic temperature control systems, by comparison, can be very complicated (and troublesome). These type of systems control both heating and cooling with a single temperature setting. The system then monitors the temperature inside your car and automatically chooses heating, cooling or a blend, as well as blower speeds to maintain the desired temperature you have chosen.

"Dual Zone" automatic temperature control systems that are offered in many newer vehicles allow the occupant of each front seat to choose their own comfort setting. One side can blow cool air and the other side can blow warm air.

AUTOMATIC TEMPERATURE CONTROL

Maintaining a relatively constant temperature setting is not as easy as it sounds because the temperature inside and outside the vehicle is constantly changing. The ambient (outside) temperature affects how much heating or cooling is required to heat or cool the incoming air to the desired temperature. Sun load can also change the interior temperature and cooling requirements.

As the air temperature inside your car gradually changes, the automatic climate control system has to compensate by altering the blower speed and temperature settings. It's a constant balancing act that requires a number of inputs and controls.

AUTOMATIC CLIMATE CONTROL COMPONENTS

To regulate the temperature inside your car, the automatic climate control system uses an ambient air temperature sensor outside the passenger compartment, one or more in-vehicle air temperature sensors (which may include an "infrared" sensor that measures the actual body temperature of you and/or your passengers), a "sunload" sensor to compensate for sunlight entering the vehicle through the glass, one or more electronic control modules, and vacuum or electronic controls for the various HVAC airflow control doors.

Most of the newer automatic climate control systems use small electric motors (actuators) to operate the airflow doors in the HVAC unit. There are 5-wire, 3-wire and 2-wire motors, all of which operate differently and must be replaced with the same type of motor. The 5-wire motors have a feedback circuit to keep the control module informed about their position. The 3-wire "smart" motors often have their own microchip to control and self-calibrate their position. The 2-wire motors are simple reversible 12-volt motors that push the airflow doors one way or the other. The controller keeps tabs on their position by running the motors full open and full closed, then counting the revolutions of the motor armature to figure their exact position. Like we said, these are complex, sophisticated systems.

Some vehicles, such as late model Chrysler minivans, have a "triple-zone" automatic climate control system. This system has separate controls for the driver, front passenger and rear passengers, and uses infrared sensors front and rear to monitor cabin temperature. It also uses a "smart" 2-wire electric motor to control all the blend air doors in the HVAC system. The motor not only operates the doors but keeps the control unit informed about its exact position. The system has 22 different control modules that communicate back and forth over a common bus network of multiplex wiring.

Another example of how complex these systems can be is Mercedes C320 dual-zone automatic climate control system. Unlike most other A/C systems that cycle the compressor clutch on and off to regulate the refrigeration circuit, this system has no clutch on the compressor. The belt-driven variable displacement compressor runs all the time and is controlled by a pulse width modulated signal from the A/C control module (more and more new cars are switching to this type of A/C system). Cooling is controlled by varying the compressor's output from 2 to 100 percent according to the cooling load on the system. Mercedes also uses a "smog sensor" to close off the outside air inlet if it sniffs hydrocarbons or other bad odors. Ten electric motors are used to control the various blend doors in the HVAC system, and a sunload sensor on the dash modifies A/C/ output to compensate for sun load. Even the engine cooling fan is also partially controlled by the climate control system, and 15 different interior control modules are used to regulate cooling within the passenger compartment.

TROUBLESHOOTING YOUR AUTOMATIC CLIMATE CONTROL SYSTEM

Troubleshooting an automatic climate control systems is usually beyond the abilities of a do-it-yourselfer because it often requires specialized training and tools. If an A/C cooling problem is not due to a fault in the refrigeration circuit (bad compressor, plugged orifice tube, low refrigerant, leaky evaporator, etc.), you can probably blame the automatic temperature control system. To find out why, tough, usually requires the use of a scan tool that can access and read HVAC codes (which ordinary engine-only scan tools cannot), and a digital voltmeter to test circuits and sensors.

Most late model automatic temperature control systems have self-diagnostic capabilities and can generate fault codes that indicate the nature of the problem. But in most cases, a technician still has to check out various components by measuring voltages, resistance, looking for opens or shorts in the wiring, etc. before he replaces an parts (in theory, anyway).

Accurate diagnosis is very important on these systems because many replacement parts can be VERY expensive. Parts like control modules can cost hundreds or even thousands of dollars to replace, depending on the vehicle application. Other parts such as sensors, switches, relays, resistors, vacuum valves, vacuum motors, electric motors and blower motors won't break the bank if you have to replace one, but the labor to install some of these parts (if you don't do it yourself) can take hours.

Tearing apart your dash and the HVAC system can be a very time-consuming and daunting task. So unless you are a very skilled do-it-yourselfer, this is one job you should let a professional do for you.

COMMON AUTOMATIC CLIMATE CONTROL PROBLEMS & POSSIBLE CAUSES:

No cooling (air blowing out of ducts is warm when it should be cool).

This could be a fault in the refrigeration circuit (bad compressor, plugged orifice valve, blown fuse or bad relay, low refrigerant or no refrigerant in system), or it could be a bad BLEND AIR door control motor inside the HVAC unit that is not routing the air through the A/C evaporator.

Temperature does not match the desired setting (too warm or too cold).

The system might have a bad interior temperature sensor, or a bad BLEND AIR door control motor inside the HVAC unit.

No air blows out of ducts when A/C or heat is turned on.

Possible causes here include a bad blower fan relay or fan motor.

Air fails to blow out of desired ducts (dash outlets, or lower outlets, or defroster outlets).

The problem here is likely a bad AIR CONTROL door motor that is not changing position to route the air to the desired outlets.

Nothing happens when you turn the automatic climate control system on.

Check the main system to see if it has blown (refer to your owner's manual for the fuse location). If blown, replace the fuse with one that has the SAME amp rating as the original. If the new fuse blows, there is a short or overload in the wiring that will have to be diagnosed and repaired.

If the fuse is okay, the control module may have died. The way to confirm this would be to hook up a scan tool to see if the scan tool can communicate with the control module. No communication would indicate a dead module or a wiring fault.

If the battery was recently disconnected or replaced, some automatic climate control systems will not operate until they are reset with a scan tool. The relearn procedure teaches the control module the positions of the various air flow control doors so it can control air flow and temperature.

More Air Conditioning Articles:

Air Conditioning Inspection Checklist

Troubleshoot Your Air Conditioning System

A/C Cooling Problem: Blows Warm Air Only No Cool Air

How To Recharge Your Car's Air Conditioner

A/C Service Equipment: What's Required To Service Today's Vehicles

MACS Recommended A/C Service Procedures (pdf file) 

A/C Compressor Failures

PAG oil recommendations

A/C Condenser Flushing

Retrofit Older R-12 A/C Systems to R-134a

Alternative Refrigerants

New Refrigerants & A/C Systems

California proposes ban on R134a sales to motorists

 Click Here To See More Carley Automotive Technical Articles

MACS Recommended Service Procedures

MACS Recommended Service Procedures 

MACS Recommended Service Procedures © MACSW December 2005 1 of 23 Revision December 2005 MACS Recommended Service Procedures Initial Customer Contact It is important to obtain information from the customer identifying the problem and any previous servicing history prior to attempting repair of the system. • Use of the MACS “Air Conditioning & Heater Customer Questionnaire” will help identify the problem. • Identify service activity on MACS “A/C – Heating – Ventilation – Cooling System Checklist.” Identification of Type of Service Mobile A/C systems are an integral part of the total vehicle and operation of engine cooling fan(s) and the A/C compressor can be controlled by the vehicles’ computer systems resulting in a direct effect on system operation. Cooling Operation • Lack of cooling can be due to many reasons including: o Compressor operation o System Refrigerant Charge and Type ƒ Contaminated refrigerant ƒ Air in system ƒ Too much oil in system ƒ Sealant in system blocking/restricting controls/screens o System controls ƒ Including temperature door movement and proper position ƒ Defective/improperly operating (setting drift) thermostatic expansion valve ƒ Restricted or missing orifice tube ƒ Defective/improperly operating compressor clutch cycling switches ƒ Defective/improperly operating evaporator temperature sensors/thermistors or thermostatic switches ƒ Defective control valves (in variable displacement compressors) o Airflow circuits ƒ Clogged evaporator core fins (or condensate screen/filter) ƒ Plugged cabin air filter MACS Recommended Service Procedures © MACSW December 2005 2 of 23 Revision December 2005 o System mode door position o System fan motor, fan clutch and electrical controls o Condenser -- Insufficient airflow, restriction and/or capacity or improper substitute o Cooling System – Insufficient radiator performance or coolant condition and level o Material between radiator and condenser o Other cooling system malfunctions such as low coolant, a stuck closed or improperly functioning thermostat, lack of or improper electric cooling fan operation, defective mechanical fan clutch, defective or incorrect pressure cap, defective or improperly operating coolant control valve, etc. • Outside air ingestion • Internally blocked components (such as condensers, orifice tubes, etc.) • Replacement parts that do not meet or exceed the performance of OEM components Heating - Defrosting Operation The basic areas to check include: • Internally restricted heater core, flow restrictors or hoses • Coolant flow/coolant pump operation • System controls o Including temperature door movement and proper position o Operation of heater engine coolant flow valve, if installed and part of system o Pulse Width Modulated (PWM) temperature control operation of heater coolant valve and control circuit if installed and part of system • Airflow circuits o System mode door function and correct travel positions o System fan motor and electrical controls Visual Inspection Mechanical • Inspect compressor drive belt o Improper compressor operation due to: ƒ Excess wear – cracked – glazed MACS Recommended Service Procedures © MACSW December 2005 3 of 23 Revision December 2005 ƒ Incorrect tension – causing slippage o Compressor clutch ƒ Indication of overheating or slipping • Due to incorrect air gap • Oil coating • Poor electrical connection or low clutch voltage • Poor electrical ground connection, loose, corroded • Wrong or improper clutch Noise or Component Failure • Inspect for worn – damaged – broken o Engine mounts o Check compressor mounting bolts and brackets for proper torque and attachment o Engine torque struts o Improper refrigerant or heater hose routing and mounting o Improper charge, refrigerant, lubricant or amount o OEM bulletins o Aftermarket sealants Condenser • Operation of engine cooling fan(s) o Improper mounting (upside down), loose or missing hardware o Excessive fan motor current draw o Broken, cracked or missing fan blades o Malfunctioning dual function pressure switches (fan operation & compressor cut-out) o Missing orifice tube • Restricted airflow o Reduced airflow due to: ƒ Foreign material in fins (bugs, grass, etc.) • Between condenser and radiator ƒ Damaged condenser fins ƒ Missing or misplaced airflow seals ƒ Improper cooling fan(s) operation MACS Recommended Service Procedures © MACSW December 2005 4 of 23 Revision December 2005 System Airflow To assure that the system is delivering maximum airflow the following areas should be inspected for blockage. • Outside air operation o Check cowl and system air intake for restrictions ƒ System air inlet location for • Debris • Plugged cabin air filter • Recirculated air operation o System air inlet ƒ Debris • Plenum-Case/Duct Assembly o Plugged evaporator inlet filter o Deteriorated foam seals at ducting in plenum connections o Evaporator case condensate drain plugged ƒ (Can result in wet vehicle carpet) Confirm There Is Refrigerant In System System Has Pressure • Determine if the system has refrigerant pressure o To prevent damage to service equipment from possible refrigerant contamination, the system refrigerant should be checked with a refrigerant identifier and sealant detector. • HFC-134a pressure is approximately the same as the surrounding temperature. At an area temperature of 75 degrees F. the stabilized system pressure with A/C system off will be around 75 psig. o If the engine compartment is hot and system is off, pressure may be slightly higher. System Has No Pressure (15-0 PSI) (Note: If service port valve seals are damaged, they may not allow the valve cores to depress properly, possibly making it appear that the system does not contain pressure when it actually does.) MACS Recommended Service Procedures © MACSW December 2005 5 of 23 Revision December 2005 A visual inspection for evidence of system lubricant on the refrigerant system component(s) surfaces generally indicates potential refrigerant leak points. If the system is empty and does not have any refrigerant pressure, there are two approaches that can be used in an attempt to identify the leak point(s). Vacuum Method • Connect a vacuum pump to the system service ports and attempt to draw the system into a vacuum. If this is successful: o With vacuum pump off determine if the system will hold vacuum (at least 10 minutes) o Determine if there is a noise from an identifiable leak point. • Sometimes reducing the system into a vacuum can result in the leak point becoming sealed and the leak point not found. To determine if there is a system leak the pressure method should be used. Pressure Method To provide system refrigerant pressure for leak detection, only a partial system refrigerant charge is required. Generally an amount equal to 20% of the total system charge will result in a saturated system pressure reading. Once the system contains both liquid and vapor refrigerant the system pressure will not increase by adding more refrigerant. (See Figure 1) The refrigerant can be added without evacuating the system since upon its removal the recycling equipment will remove the air during the recycling process. Adding refrigerant to a system that did not have pressure will result in a slightly higher pressure as compared to pure refrigerant in the system. MACS Recommended Service Procedures © MACSW December 2005 6 of 23 Revision December 2005 Partial Refrigerant Charge 0 20 40 60 80 100 120 Refrigerant Service Fitting Pressure High/low side No Vacuum Prior Vacuum Pure Refrigerant Refrigerant & Air Saturated System Pressure with liquid/vapor at 85 degrees F. Figure 1 • With at least 50-psig system pressure perform the leak checking process. • If the refrigerant system is to be operated, install the full factory charge amount. Performance Testing Upon completion of the initial visual inspection and determination as to whether or not the system has pressure, it would be best at this time to conduct a system performance test. Running a performance test can offer an opportunity to see if the system will cool properly after repair(s) have been performed. It may also help eliminate possible future concerns and questions. If it has been determined that the system has a functioning or somewhat functioning compressor, a sufficient charge of refrigerant should be added to enable the compressor to operate to complete a performance test of the system. The performance test may also allow the technician to note if the compressor is functioning properly, if the compressor is noisy, if the expansion valve is functioning, if there is the expected temperature drop at the condenser, if there may be air blend door issues, or if the system may have any additional cooling issues. Having a sufficient MACS Recommended Service Procedures © MACSW December 2005 7 of 23 Revision December 2005 charge of refrigerant in the system will also ensure the system contains adequate internal pressure for use of an electronic leak detector. If fluorescent dye is to be used in a leak detection process, it may also be added at this time. System Refrigerant Leakage System refrigerant leaks can occur in many locations where they may be difficult to visually pinpoint. Visual inspection for evidence of system lubricant generally indicates potential refrigerant leak points. When a point is identified, use an SAE certified leak detector to verify the leak. Except for compressor shaft seals, surfaces that have evidence of lubricant generally indicate the presence of a refrigerant leak. In some cases, even though there may be a sign of lubricant leakage at a compressor shaft seal, the leak may be too small to result in a sufficient release of refrigerant which could be identified with a leak detector. The condenser, evaporator and rigid pipes/tubing, unless physically damaged, will not usually experience leakage. However, these components can be susceptible to corrosion, which could result in leakage. In general, operational leakage or mis-assembly of the following system components can result in system leak points. • Coupled flexible hose(s) o At hose and metal coupling connection o At quick connect points if moved • Compressor o Shaft seal o Porous casting/shell case seals o Pressure switches and/or o-rings o Pressure relief valve • System service ports due to: o Missing or lost service caps o Leaking/damaged core valves MACS Recommended Service Procedures © MACSW December 2005 8 of 23 Revision December 2005 • All refrigerant coupling points o O-Rings ƒ Cut/damaged ƒ Wrong size O-ring (diameter, thickness) ƒ Residual flush material, sealants, alternate refrigerants o Flat surface seals – gaskets ƒ Cut/damaged ƒ Incorrect torque of connections ƒ Residual flush material, sealants, alternate refrigerants Identification of System Refrigerant Leakage Identification of a small system refrigerant leak may require a combination of leak detection methods. If a system has at least 50-psig pressure, the system can be checked with an electronic leak detector. It should be noted that there is a major difference between the capabilities of electronic refrigerant leak detectors to find small leaks even though they are certified to the SAE standard. Increasing System Refrigerant Pressure for Leak Detection Elevating the temperature (warming) of all the A/C system components will help increase the system pressure for leak detection. (It is preferred to work on vehicles when the ambient temperature is above 70 degrees F.) Increase System Refrigerant Pressure Procedure (Using Engine Heat) • A/C System Controls o Turn compressor off so it will not operate. (Note: On some vehicles, particularly those equipped with Automatic Temperature Control systems, this may not be possible. It may be necessary to electrically disable the clutch by removing the clutch control relay, disconnecting the clutch field coil’s electrical connector, removing a fuse, etc. Also, some vehicles are equipped with clutchless compressors. Clutchless compressors operate any time the engine is running. If a vehicle is equipped with a clutchless compressor, refer to the vehicle manufacturer’s service information to see if a procedure exists to operate the engine without the compressor also operating.) MACS Recommended Service Procedures © MACSW December 2005 9 of 23 Revision December 2005 • Set panel system controls o Outside air (not max or recirculated) o High fan speed o Airflow from panel outlets o Temperature position max cold • Vehicle hood open to allow warm engine air to enter cowl inlet to A/C system • Operate engine idle condition o Neutral (park) with parking brake applied ƒ Depending on engine compartment temperature ƒ Run engine to warm up A/C system components for 15 minutes o After idling engine for 15 minutes (hot condition) o Shut engine and A/C fan off and start the leak detection process Other Leak Detection Methods Soap Bubbles Using soap bubbles to detect a leak will only identify a large leak. A leak rate producing 1 bubble per second results in a loss of over 50 ounces per year. Since most mobile systems contain only one half of that amount, they will lose cooling capability within days. As noted in figure 2 the typical R134a single evaporator system charge is 25.6 ounces. The information found in figure 2 compares the detection rate of an SAE leak detector of 0.5 ounces per year with water and soap bubble detection methods of 45 to 55 ounces per year. The use of soap bubbles may help in verifying the location of large leaks in tight and hard to access places or near multiple refrigerant connections. Unless the system has a large refrigerant leak, using soap bubbles for leak detection is an ineffective method when servicing mobile A/C systems. MACS Recommended Service Procedures © MACSW December 2005 10 of 23 Revision December 2005 Refrigerant Leak Detection Capability 0 10 20 30 40 50 60 WATER BUBBLE SOAP BUBBLE J1627 SAE SPEC. Refrigerant Loss Ounces/year Identifiable Leak Rate 1 bubble per second SAE Identifiable Leak Rate 0.5 ounce [14g] per year Average Single Evap. System Charge 2000 - 2004 MY 25.6 Ounces Figure 2 Using Nitrogen Using nitrogen for leak checking is a questionable method due to a lack of nitrogen detection equipment and nitrogen’s high pressure. For example, if an evaporator core is subjected to over 300 PSI, it may burst. As the components age, they may fail at pressure less than 300 PSI. Nitrogen and soap bubbles have been used in the commercial refrigerant industry on large systems that are prone to high leakage rates. Using nitrogen and soap bubbles for locating small leaks in mobile A/C systems is of questionable value. Using Other Refrigerants The use of R22 or other chemicals having higher pressure can result in system damage. Use of R22 for leak checking can result in chemical damage to the system over time (especially to seals). The R22 cannot be completely removed from the system after leak checking. MACS Recommended Service Procedures © MACSW December 2005 11 of 23 Revision December 2005 The R22 remaining in the system’s lubricant may over time chemically damage hose and seal material resulting in a potential later system failure. Using R22 is never recommended for use for leak checking. Check system and/or component manufacturers' policy on using other refrigerants. Using Trace Dye When trace dye is installed in the system it requires that the lubricant carry it to the leak point. This may not be an immediate action and may require hours of system operation, depending upon the system’s use, before the dye will be visible when using a test lamp. Dye installed in the system may not be visible depending upon its original expected lifetime and its visibility can be reduced after being exposed to air (point of leak) and may not be identifiable the next season. If too much dye is added to the system, it can affect compressor durability by changing the lubricating ability of the system’s oil and restricting oil flow through the refrigerant system. Using Vacuum Decay Using a vacuum decay method will only confirm you have a leak. Unless very large, it does not give the location. You may also have a leak in your measuring equipment. In addition, using a vacuum decay method may not find some leaks, because when the system is under vacuum the leak point (o-ring – seal – hose) may seal and leak only when under pressure. Electronic Detector Component Leak Checking • Leak test with the engine off o Do not contaminate the detector probe tip with dirt, grease or expose it to a direct stream of refrigerant. o If component being checked is dirty, wipe it off with a clean shop towel or blow off with dry shop air. ƒ Do not use cleaners or solvents. • Detectors may react to their chemical composition. ƒ Leak test the entire refrigerant system, testing all lines, fittings and components. • If a leak is found, continue to test the remainder of the system for potential additional system leaks. ƒ Move the probe around the location, at a rate no more than 25 to 50 mm/second (1 to 2 in/second), MACS Recommended Service Procedures © MACSW December 2005 12 of 23 Revision December 2005 ƒ Hold the sensing probe no more than 5 mm (1/4 in) from the surface completely around the area being checked. • Moving the sensing probe slowly and as close as possible to the component improves the chance of finding a leak. ƒ Confirm the leak by blowing shop air into the area of the suspected leak to disperse any refrigerant that may not be due to the suspected leak. • Repeat if necessary. • Blowing out the area with shop air often helps locate the exact position of large leaks. • Leak testing of evaporator core o Run the air conditioning blower on high speed for 15 seconds minimum. ƒ Turn blower off, wait 5 minutes for the refrigerant to accumulate in the case. • Insert the leak detector probe into the o Blower resistor block opening or o Evaporator case drain hole if there is no condensation, or o Since refrigerant is heaver than air, locate the lowest point in the duct system. Do not rely on an indication of a leak with the probe located in panel outlet. o Into the closest opening in the heating/ventilation/air conditioning case to the evaporator. ƒ If the detector alarms, an evaporator leak has apparently been found. ƒ (Note: On R12 systems there will be a covering of oil and dirt on the evaporator. On R134a systems there may not be since the lubricant is water soluble. Therefore check condensate drain for dye products.) Leak Detectors Meeting SAE J1627 Depending upon the technology used for a leak detector, false triggering may occur from foam seals and adhesives used around the evaporator. Some detectors meeting J1627 are calibrated to detect only R12 and R134a refrigerants, thus eliminating the possibility of false leak identification. MACS Recommended Service Procedures © MACSW December 2005 13 of 23 Revision December 2005 System Lubricant Charge There is no effective way in the field to determine the amount of lubricant that is in a system. Systems with too much oil can result in reduced cooling capacity. Excessive lubricant results in the internal coating of the evaporator or condenser resulting in less heat transfer. Only the A/C system and component manufacturer’s recommended lubricant type, viscosity and amount should be used to provide the maximum cooling performance and compressor durability. To establish the correct amount of lubricant in a system, each component must be drained or liquid flushed (using approved chemicals and procedures) and the manufacturer's recommended lubricant amount for the specific system be added. System Refrigerant Charge The system pressure cannot be used to determine the amount of refrigerant in a system. To assure that the system is operating properly, the refrigerant should be recovered from the system and the correct amount installed with properly calibrated charge equipment. “Top Off” service procedures will result in improper refrigerant charge amounts and is not considered professional servicing. Establishing System Refrigerant Charge Amount Mobile A/C systems are operated over a great variation of system loads, from low loads to hot weather soak and cooldown conditions. To assure that a continuous source of liquid refrigerant is supplied to the expansion device, the vehicle manufacturer establishes the charge amount for high load conditions. When the system refrigerant charge amount is determined, several factors are included in the selection of the charge value to ensure system performance. These factors include small losses from servicing procedures and lubricant circulation in the system. Mobile A/C system refrigerant charging should not be attempted by using high and low side pressure readings. Using high and low side pressure readings are commonplace for charging commercial systems, since they generally operate under constant load conditions. Unlike commercial A/C systems, on any given day, a mobile A/C system could be required to operate from hot vehicle soak and cooldown to reduced stabilized MACS Recommended Service Procedures © MACSW December 2005 14 of 23 Revision December 2005 highway cooling demand conditions. Under all these conditions, an adequate amount of liquid refrigerant must be available to provide maximum system cooling performance. TXV System A typical expansion valve system can be found in figure 3. The TXV can either be a separate in-line device or a block valve located near the evaporator. Figure 3 The charge curve identified in figure 4 shows the variation in system pressure under high load conditions for a production system. The factory system charge was established at 28 ounces. For this condition the system pressure change between 22 to 28 ounces of refrigerant in the system was 5-psig on the high side and 4-psig on the low side. Depending upon the temperature in the service bay and the load on the A/C system, it is impossible to duplicate charging conditions that rely upon pressure reading for every type of mobile A/C system serviced. Using the pressure values identified on the left side of the flat portion charge curve, charging to 295-psig high side and 22-psig low side could be in the range of 22 ounces. With only a slight system refrigerant loss the system would have reduced cooling performance and the potential for inadequate system lubricant circulation. Charging to MACS Recommended Service Procedures © MACSW December 2005 15 of 23 Revision December 2005 the right side of the charge in the 30 to 32 ounce range could result in the system being shut off on a hot day in city traffic. Since the capacity of the receiver-drier limits the amount of excess refrigerant that can be added to the system, systems that incorporate the integral receiver-drier/condenser design have less internal refrigerant storage capability as compared to a separate RD system. The correct factory refrigerant charge is required to avoid overcharging the system. System Charge Curve 108F Ambient 40 MPH 78 65 61 61 60 60 58 57 16 20 22 24 26 28 30 32 225 260 295 295 295 300 310 345 0 50 100 150 200 250 300 350 16 20 22 24 26 28 30 32 Ounces R134a Outlet Temperature Suction Pressure Head Pressure System Charge 28 Ounces Head Pressure PSIG Suction Pressure PSIG Panel Outlet Temperature Degrees Figure 4 Refrigerant Overcharge Symptoms A typical system overcharge problem may not be evident on a cool morning or in the service bay during low heat load conditions. Excess refrigerant will result in increased high side system pressure, when the system is operated during high heat load conditions. The excessive pressure will cause the high side pressure switch to shut off the compressor when conditions such as idle and stop and go driving are encountered. Although an electric or mechanically engine driven fan should be operating during low speed operation, the amount of airflow may not be enough to handle the heat load. Considering that most passenger cars and light trucks have electric engine cooling fan(s), during idle conditions, the effect of wind can influence airflow through the condenser. Side or tail wind during city traffic and idle conditions can result in loss of A/C system cooling due to the pressure discharge (PD) switch shutting off the MACS Recommended Service Procedures © MACSW December 2005 16 of 23 Revision December 2005 compressor. At road speeds, increased airflow over the condenser allows the compressor to re-engage, but may still result in higher discharge pressures, causing warmer outlet air temperatures. Orifice Tube System A typical orifice tube system can be found in figure 5. Figure 5 The charge curve in figure 6 is for an orifice tube system having a factory refrigerant charge of 26 ounces. As compared to the TXV system, the high side curve is more gradual as additional refrigerant is added. This is due to the refrigerant being stored in the accumulator on the low side of the system. MACS Recommended Service Procedures © MACSW December 2005 17 of 23 Revision December 2005 Figure 6 With professional service equipment, less time will be consumed installing the correct system refrigerant charge, ensuring the proper operation of the A/C system as compared to charging by questionable gauge pressure readings. Not being able to identify how much refrigerant is in the system results in the potential for improper system operation. Systems that are overcharged become an environmental concern due to the potential release of the excess refrigerant. Systems not having the correct refrigerant charge may result in many unseen problems. Low refrigerant charge can result in: Poor system performance; evaporator core refrigerant distribution problems can result in temperature spread across panel outlets and localized core icing (freeze up), reducing system airflow. Reduced cooling performance will occur due to a lack of solid flow of liquid refrigerant (partial vapor) being supplied to the evaporator under high loads. Since lubricant circulation in the system relies upon a proper system refrigerant charge, inadequate refrigerant and lubricant will result in increased compressor operating MACS Recommended Service Procedures © MACSW December 2005 18 of 23 Revision December 2005 temperature and potential compressor failure. In addition, the excess temperature can result in damage to the lubricant, flexible hoses and seals. Not all lubrications are compatible with a mobile A/C system. There are some lubricants which will not be transported in sufficient quantities to service the compressor. The information found in figure 7 compares a reduced system refrigerant charge’s effect on the compressor discharge temperature. This is something that is not identifiable by just looking at the system operating pressures. The production charge for this system is 26 ounces. By reducing the charge by 6 ounces (to 20 ounces) the high side pressure was reduced by 21 psig (from 239 to 218) and the low side pressure was 6 psig lower (from 38 to 32). Panel outlet temperature is four degrees cooler with the 6 ounce reduced charge (58 vs. 62). Unfortunately, when charging the system by using the pressure and panel outlet temperature, a reduced system charge could occur. The undetectable temperature problem is the compressor outlet temperature, which increased from 150 F to 182 F for the reduced 6-ounce charge, and with a reduced charge of 8 ounces was 204 degrees F. Figure 7 MACS Recommended Service Procedures © MACSW December 2005 19 of 23 Revision December 2005 Compressor Failure Should a system experience an internal compressor failure, it may not be possible to completely clean the system of the debris from the failure. Since heat exchangers (evaporator/condenser) have very small multiple internal passages and internal baffles, flushing may not clean all passes returning the heat exchanger to its expected level of performance. Replacement of an orifice tube or replacing the expansion valve must be done to assure maximum performance. Replacement of the accumulator or receiver dryer is necessary when an internal compressor failure has occurred. Flushing of flexible hoses and refrigerant lines is may be required as well as the installation of auxiliary filters or compressor screens. Hose assemblies having inline mufflers should be replaced, since flushing may not remove all the debris from the failure. Liquid lines that contain permanent orifice tubes must be replaced. Installation of non-restrictive inline filters minimizes the chances of the re-circulation of any foreign material remaining in the system. Movement of debris can reverse flow from the system high side to low side when the system is shut off and equalizes, resulting in the contamination of low side components (the accumulator and evaporator). Refrigerant Removal It is extremely difficult to completely remove all refrigerant from the system. When the system is being evacuated, the refrigerant boiling (changing from liquid to vapor state) results in cooling of the system components. The lubricant also adsorbs the refrigerant and the evacuation process is slow in removing the refrigerant from the lubricant. Raising the temperature (warming) of all the A/C system components and reducing the system to at least 20 inches of vacuum, will help recover the maximum amount of the refrigerant in the shortest period of time. Removal Procedure o Turn off the compressor so it will not operate. (Note: On some vehicles, particularly those equipped with Automatic Temperature Control systems, this may not be possible. It may be necessary to electrically disable the clutch by removing the clutch control relay, disconnecting the clutch field coil’s electrical connector, removing a fuse, etc. Also, some vehicles are equipped with clutchless compressors. Clutchless compressors operate any time the engine is running. If a vehicle is equipped with a clutchless MACS Recommended Service Procedures © MACSW December 2005 20 of 23 Revision December 2005 compressor, refer to the vehicle manufacturer’s service information to see if a procedure exists to operate the engine without the compressor also operating.) • Set panel system controls o Outside air (not max or recirculated) o High fan speed o Airflow from panel outlets • Vehicle hood open to allow warm engine air to enter cowl inlet to A/C system • Operate engine idle condition o Neutral (park) with parking brake applied ƒ Depending on engine compartment temperature • Run engine to warm up A/C system components for 15 minutes • After idling engine for 15 minutes (hot condition) • With engine idling and A/C fan high, system on outside air, start refrigerant recovery process • When refrigerant recovery is completed, including the required 5 minute recheck for system pressure (system refrigerant out gassing), shut vehicle and equipment off. Desiccant Replacement The purpose of desiccant in a mobile air conditioning system is to absorb and hold moisture. Moisture in a system (above an acceptable level) can lead to corrosion and degradation of the lubricant. The general industry recommended desiccant replacement service guidelines are found in table1. Desiccant material is located in the refrigerant circuit. Servicing of the desiccant will depend upon its location. The location may not allow the replacement of only the desiccant material, resulting in the replacement of an accumulator, or a receiver drier assembly. Systems having an integral receiver drier condenser assembly may have the service feature that allows replacement of the desiccant pack. MACS Recommended Service Procedures © MACSW December 2005 21 of 23 Revision December 2005 Table 1 Recommended Guidelines for Replacement of Desiccant Service Operation Replace RD/Accl or Desiccant Pack Yes w/Replace Compressor (Ref System contains foreign material) X w/Replace Evaporator (Ref System contains foreign material) X w/Replace Condenser (Ref System contains foreign material) X w/Replace refrigerant line or hose (Ref System contains foreign material) X w/Replace Refrigerant Control OT/TXV (Ref System contains foreign material) X w/System has open line(s) more that 24 hours X w/System has operated over 5 years without desiccant replacement in high humidity area X w/System has operated over 10 years without desiccant replacement X Desiccant Replacement Guidelines Desiccant replacement guidelines vary among vehicle manufacturers and system, component and parts suppliers. To maintain the warranty on purchased parts, desiccant must be replaced as specified by the particular supplier whose parts are being installed. Flushing Systems Flushing of the mobile A/C system may not completely remove all potential foreign material from the system. Proper use of flushing solvents is important to accomplish the desired results. It is necessary to purge all residual flush material from the system when servicing. Any residual flush left behind will contaminate and dilute the A/C system oil charge. SAE standard J2670 provides testing and acceptance criteria for stability and compatibility of chemicals, including flushing materials and additives intended for use in R134a vehicle air conditioning systems. Use of non-compatible chemicals may result in future (extended time) failure of A/C system materials. MACS Recommended Service Procedures © MACSW December 2005 22 of 23 Revision December 2005 Flushing Material R134a is commonly used as a flushing solvent in conjunction with equipment capable of handling the refrigerant in such a manner. Because R134a can act as both the refrigerant and a flushing solvent, R134a is deemed to meet all the requirements set forth in the J2670 specification. Keep ion mind that R134a should only be used to flush lubricant and loose debris from an A/C system. R134a will not remove any particulate matter that has attached itself to the inner tube walls. Some A/C system and component manufacturers have developed flushing solvents and equipment for removal of foreign material from the system. In general, flushing provides a method of removing: -- Lubricant -- Residual materials found in the system -- Foreign material Removal of some foreign debris may not be achievable in heat exchangers due to the multipath circuits and the potential for the flushing procedure to bypass the plugged refrigerant flow path. To achieve the original level of performance, replacement of the heat exchanger may be required. In flushing a contaminated system, follow the procedures provided by the system or component manufacturer and by using the recommend flushing material and equipment. Evaporator Freeze Protection Loss of system cooling performance can occur if the system has an incorrect evaporator freeze protection setting. This condition can occur when the system has been operated for an extended period of time. When the evaporator fin surface is operated below 32 degrees F, the collected condensate water will turn to ice. This will then result in loss of system airflow as the frozen water blocks the air passages and the icing condition continues to spread over the core area. With an incorrect control setting, this loss of cooling can occur on systems that use a fixed displacement or variable displacement compressor. There are many options on how evaporator freeze protection is achieved. Some of the control methods include pressure control devices in the compressor body or attached to other refrigerant system MACS Recommended Service Procedures © MACSW December 2005 23 of 23 Revision December 2005 components. Other options include electronic sensors or thermal switches controlling compressor operation by sensing refrigerant component surface or outlet air temperature. It is important to identify how the system manufacturer controls evaporator freeze protection and that the correct pressure or temperature settings are used when servicing the system. AIR CONDITIONING & HEATING CUSTOMER QUESTIONNAIRE _______________________________________________________ CUSTOMER Name__________________________ Phone__________________ Date__________ Address________________________ City______________ State_____ Zip_______ _______________________________________________________ VEHICLE Year____________ Make____________ Model____________ Color____________ A/C System Type – ❒ Manual ❒ Auto. Temp. Control ❒ Dual / Rear Auxiliary Unit _______________________________________________________ PROBLEM / SYMPTOM ‰ No A/C ‰ No Heat ‰ No Defrost ‰ Poor Cooling ‰ Poor Heating ‰ Improper Fan/Blower Operation ‰ Air From Wrong Outlet(s) ‰ No Temperature Control ‰ Noise Inside Car ‰ Noise Under Hood ‰ Interior Water Leak ‰ Engine Coolant Leak ‰ Warning Light(s) On ‰ Odor ‰ Other* (See Below) WHEN DOES THE PROBLEM OCCUR? ‰ Always ‰ Intermittent ‰ When Hot ‰ When Cold ‰ At Start Up ‰ During Warm Up ‰ At Idle ‰ High Engine Speeds ‰ Driving Away From Stop ‰ At Road Speeds Have there been any previous attempts to repair this problem? ❒ No ❒ Yes If there were previous repair attempts, what was done? (What parts were installed, etc.) _____________________________________________________________________________ _____________________________________________________________________________ Did previous repairs help the problem? ❒ No ❒ Some ❒ A lot ❒ At first, but not now. Have repairs or service of any kind been recently performed to the vehicle? ❒ No ❒ Yes If so, exactly what was done? ______________________________________________________________________ ______________________________________________________________________ *FURTHER DESCRIPTION OF THE PROBLEM ______________________________________________________________________ ______________________________________________________________________ 

Air Conditioning Best Service Practices

Air Conditioning Best Service Practices Tried & Tested

When your car or truck has an air conditioning problem and needs service, what should you do? If your A/C system only needs some refrigerant, you can probably recharge the a/c system yourself. But if you are having cooling problems, leaks or electronic control problems, you should probably seek out a repair facility that specializes in air conditioning service work.

Our advice is to seek out a repair facility that is a member of MACS, the Mobile Air Conditioning Society. MACS is a non-profit trade association for repair shops that do air conditioning service work. MACS promotes training, education, professionalism, and most importantly "Best Practices" for servicing and repairing your vehicle's air conditioning system.

Since 1991, MACS has assisted more than one million technicians to comply with 1990 Clean Air Act requirements for certification in refrigerant recovery and recycling to protect the environment.

Recently, the Climate Protection Partnership division of the U.S. EPA teamed up with MACS to publish and promote six mobile air conditioning best service practices checklists. These checklists are written for professional technicians to help them environmentally safe and technically proper air conditioning service and repairs. The purpose of the checklists is make sure your vehicle is serviced correctly when you take it in for air conditioning service work.

If your shop is NOT following these practices, you should bring it to their attention - or take your vehicle to another shop who does follow the Best Practices recommendations.

Note: The Best Practices guidelines are voluntary recommendations, and are not required by law. Even so, they do reflect current thinking on the best ways to properly service and repair automotive mobile A/C systems. The input for these checklists was provided by highly experienced A/C technicians who are familiar with the right ways and wrong ways of servicing service A/C systems.

The A/C Best Service Practices Guidelines for A/C service include:

A/C Service (general)
Leak Detection
Refrigerant Recovery
System Charging
Field Repair and Assembly of A/C Hoses
A/C Equipment Maintenance.

 Click Here for MACS Air Conditioning Best Practices Guidelines

More Air Conditioning Articles:

MACS Recommended A/C Service Procedures (PDF file). 

Flammable Refrigerants

A/C Cooling Problem: Blows Warm Air Only No Cool Air

Troubleshooting Air Conditioning Problems

Troubleshoot Automatic Climate Control 

Troubleshooting A/C Cooling Problems with Temperature

Cooling Fan (electric)

Cooling Fan Relay Problems

How To Recharge Your Car's Air Conditioner

Refrigerant Contamination 

Alternative Refrigerants for R-12

New Automotive Refrigerants 

California proposes ban on R134a sales to motorists

Information about Retrofitting older vehicles with R-12 A/C systems to R-134a

A/C Compressor Failures

A/C Condenser Flushing


 Click Here To See More Carley Automotive Technical Articles

R-12 to R-134A Refrigerant Retrofit

R-12 to R-134A Refrigerant Retrofit

If you drive an older vehicle (pre-1994), the air conditioning system contains R-12 refrigerant (Freon). As long as the A/C system has no leaks and it cooling normally, there is no need to convert from R-12 to the new "ozone safe" R-134a refrigerant. But if your A/C system has lost it's charge because of a leak, collision damage, or the need to open it to replace a compressor, hose or other component, you may have to convert from R-12 to R-134a when you recharge the system

Why? Because R-12 is no longer produced in the U.S. Supplies of recycled R-12 still exist, and some R-12 is still brought in from offshore suppliers. But it is hard to find and expensive. That's why many people simply recharge their older R-12 air conditioning system with R-134a after repairs have been made.

R-134a Retrofit Conversion Costs

Does it make economic sense to retrofit an older vehicle to R-134a if the A/C system has lost its refrigerant charge or needs major repairs? The older a vehicle gets, the more it depreciates. By the time it is 15 or more years old, it may only be worth a few hundred dollars. Many owners will not put any more money into an older vehicle unless the repairs are absolutely necessary to keep it running. Even then, it may be less expensive to get rid of the vehicle or to junk it than to fix it up. Even so, A/C is something that's hard to do without especially during hot weather. Hot summer temperatures and high humidity can make driving in city traffic unbearable.

A professional retrofit by a repair shop can cost hundreds of dollars, depending on what they do. But on many older vehicles, you can save money and do the job yourself - if you have some know-how and the right equipment.

WHEN R-134A RETROFIT MAKES SENSE

There is NO reason to retrofit a vehicle to R-134a as long as the R-12 system is cooling properly and contains a normal charge of refrigerant. A/C systems designed to use R-12 will cool best when charged with R-12 refrigerant. Even if the system leaks, repairing the leaks and recharging it with R-12 is usually the best repair alternative. Converting to R-134a typically reduces cooling performance somewhat, and may require some additional modifications depending on the vehicle model year.

Where retrofit makes the most economic sense is when an A/C system requires major repairs such as a new compressor, condenser or evaporator.

The average repair bill to retrofit when other A/C repairs are needed, according to the Mobile Air Conditioning Society (MACS), is about $100 over and above any other repairs that may be needed (such as replacing the compressor, condenser or evaporator, etc.). The cost to retrofit usually does not add that much to the total repair bill because converting 1990s vintage vehicles to R-134a in most cases is fairly easy and does not require many (if any) changes. If the vehicle has barrier style hoses and the compressor and seals are compatible with R-134a, the only thing that has to be changed is the compressor lubricant.

TWO WAYS TO DO A R-134A RETROFIT

A retrofit can be done one of two ways. The first is to follow the vehicle manufacturer recommended retrofit procedure. This generally involves removing all the old mineral oil from the system, replacing the accumulator or receiver/dryer with one that contains X-7 desiccant, replacing O-rings (if required), installing or replacing a high pressure cutout switch (which many shops seem to forget), changing the orifice tube or expansion valve (if required), then adding the specified PAG oil and recharging the system with R-134a. On some applications, installing a more efficient condenser may be recommended for improved cooling performance. After the modifications are made, the system is recharged to about 85 to 90% of its original capacity with R-134a.

Federal law also requires the permanent installation of R-134a fittings on the high and low service ports to reduce the chance of refrigerant cross-contamination the next time the vehicle is serviced. Labels must also be installed to identify the system has been converted to R-134a.

Installing service fitting adapters allows R-134a to be put into a R-12 system.

The other approach to retrofit is the "quick and cheap" one. On many 1989 through 1993 vintage vehicles, R-12 A/C systems can be converted by simply recovering any refrigerant that is still in the system, adding POE oil (which is compatible with both types of refrigerant), and recharging to 85 to 90% capacity with R-134a.

A simple retrofit may therefore cost no more than a few cans of refrigerant and some compressor oil -- provided there's nothing else wrong with the A/C system. But simple low cost retrofits may not give the best cooling performance, and may not even be possible on some vehicles. Any compressor that has Viton seals is not a candidate for retrofit. This includes original equipment compressors such as Tecumseh HR980, some Keihin compressors and some Panasonic rotary valve style compressors on older Japanese cars. On these, the compressor must be replaced.

Compressor durability is also a concern with some vehicles. Because R-134a raises compressor discharge pressures and increases the compressors work load, some lightweight compressors may not be rugged enough to tolerate R-134a over the long haul. This applies to the Harrison DA6 and Ford FX-15 compressors. The Harrison DA6 can be replaced with a HD-6, HR-6 or HR-6HE compressor. The Ford FX-15 compressor can be replaced with a FS-10 compressor.

Regardless of which retrofit method is used, cooling performance will vary depending on the design of the system. As a rule, expect anywhere from a 3% to 15% decrease in cooling performance when an R-12 system is converted to R-134a. Systems with relatively large or efficient condensers will experience less of a drop in cooling performance with R-134a than those with smaller or less efficient condensers.

ADDITIONAL R-134A RETROFIT TIPS

One way to improve cooling performance when retrofitting an older R-12 system to R-134a is to install a "variable valve" orifice tube in place of the standard fixed orifice tube. These aftermarket variable orifice tubes allow the flow rate through the valve to change for better cooling at idle and low speeds. Such a valve can lower the A/C outlet air temperature by as much as 5 to 8 degrees, which can make quite a difference if the vehicle is crawling along in stop-and-go city traffic.

Adding an extra cooling fan can help boost cooling performance, especially at idle and low speeds. Many older rear-wheel drive cars and trucks do not have a separate electric fan for the A/C condenser. They rely solely on the belt-driven fan for cooling, which may not be adequate in extremely hot weather with R-134a. Installing an auxiliary fan that comes on when the A/C is turned on give provide the extra airflow needed to carry away the heat.

Installing a larger or more efficient condenser can also help compensate for losses in cooling efficiency with R-134a. If the original condenser or evaporator is being replaced because of a leak, damage or defect, make sure the replacement unit has the same or better BTU rating. Some aftermarket replacement condensers and evaporators may not deliver the same cooling performance, and create a problem you did not have before.

When a compressor fails, it can throw metallic debris into the system. Most of the junk ends up in the bottom of the condenser, but some of it can also be blown back into the suction hose. Flushing the condenser, hoses and evaporator with refrigerant or an approved solvent may remove most of the debris, but parallel flow condensers cannot be flushed effectively. Replacement is often recommended if debris is found in the system. Most experts also recommend installing an in-line filter (high side and/or low side) to protect the replacement compressor and orifice tube or expansion valve. There are also filter screens that can be installed in the suction line to prevent any debris from reentering the compressor, too.

ALTERNATIVE REFRIGERANTS

The vehicle manufacturers still do not approve of any alternative refrigerants other than R-134a for retrofit, though a variety of alternative refrigerants currently meet the EPA SNAP (Significant New Alternatives Policy) rules for environmental acceptance. Most of these are blends that are formulated to replace R-12 in older vehicles.

It is important to remember that R-134a or any other alternative refrigerant cannot be mixed with R-12 or used to top off an R-12 system. If an A/C system still contains any R-12 at all, it must be removed using approved recovery equipment (venting is not allowed) before a new refrigerant is added to the system. This is an absolute must to prevent cross-contamination of refrigerants and cooling performance problems.

Mixing different refrigerants can cause big problems. For one, it will increase the system operating pressure. This can result in a loss of cooling performance and may overtax the compressor to the point where it fails. R-134a and mineral oil will not mix. So if somebody recharges an R-12 system with R-134a and does not add a compatible lubricant, the compressor will soon fail.

• 57% had R-12 and R-134a mixed together (up 10% over last year).
• 20% had R-22 in R-12 systems.
• 20% had two or more refrigerants mixed together (down 10% over last year).
• 30% contained hydrocarbons (propane or other flammable hydrocarbons).
• 2% had too much air.

The same survey also revealed that only one out of 10 technicians knew about EPA SNAP rules, the Significant New Alternatives Policy regulations that prohibit refrigerant venting, require recovery and recycling, prohibit the intermixing of different refrigerants or the use of flammable refrigerants.

Two out of five technicians also did not know the service fittings on an A/C system MUST be changed if the system is converted from R-12 to R-134a or anything else. And three out of five technicians did not know mixing R-12 and R-134a could cause problems.

For more information about the usage of Alternative Refrigerants, see Alternative Refrigerant Report

Click Here for info about A/C R-134a Retrofit Guide 

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How To Recharge Your Car's Air Conditioner

Refrigerant Contamination 

Alternative Refrigerants

New Automotive Refrigerants 

Flammable Refrigerants

California proposes ban on R-134a sales to motorists

MACS Recommended A/C Service Procedures (PDF file - requires Adobe Acrobat Reader to view).

A/C Compressor Failures

A/C Condenser Flushing


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