Where is the orifice tube on a 1991 chevy silverado
Since about mid-year 1991, the orifice will be in the lower line on the condenser, so you'll have to remove the grille to access it.
Early 1991-back to 1988, it was in the lower line off the evaporator.
The orifice tube restricts the flow of refrigerant to the evaporator. This restriction allows high pressure liquid Freon to change into low pressure Freon before entering the evaporator. The orifice tube is located inside the hose running between the condenser and the evaporator. You'll need an orifice tube removal kit if you are looking to remove it.
Its not that cut and dried, First you will need the refrigerant recovered, then take the old one out. It should be in the small line entering the evaporator. Take it out, if there is metal shavings on it, then you need to replace the compressor and flush the condenser, or replace the condenser. the short end (looking at the o-ring) goes in towards the rear of the car. Then you will need sit evacuated with a vacuum pump and recharged with the proper amount of refrigerant and oil. Its really a job for a A/C shop.
Click the link below to view the exact location
The "O" tube does not wear out or need replacing unless the compressor has failed and there is metal in the system. That being said this is the location and procedure to replace the "O" tube
REMOVE OR DISCONNECT
Discharge and recover refrigerant from the system.
Right turn signal and park lamp assembly.
Grille retaining screws.
Grille.
Evaporator tube (75) and O-ring (76) from condenser (5).
Expansion tube (3).
INSTALL OR CONNECT
Expansion tube (3).
Evaporator tube (75) and new O-ring (76) to condenser (5).Tighten;
Evaporator tube (75) to 24 Nm (18 ft. lbs.) .
Grille.
Grille retaining screws.
Right turn signal and park lamp assembly.
Refrigerant to the system.
Check the system for leaks.
As I remember the orifice tube on your 1992 GMC pick up is behind the front grill at one of the condenser fittings. The grill is not that hard to remove. You must remove the park light assemblies to access screws behind them. There are other screws located across the top and in the center. Look carefully to find them all. There are also some clips along the bottom to release. Once you start looking it will all make sense. Before removing the grill look for a wide spot in one of the ac lines so that you can be fairly sure that is were the orifice tube goes.
