1979 Oldsmobile Cutlass Air Conditioner not working

BRM.11

MEMBER
1979 OLDSMOBILE CUTLASS
6 CYL
2WD
AUTOMATIC
89,000 MILES

I recently purchased this cutlass. Tha AC has not worked. I found the plug that connects to the compressor was unhooked. When I plugged it into the compressor I still get nothing. I am getting 12 volts to the green wire on the plug when the the thermostat & switch are on. How can I know if my issue is a compressor issue without purchasing a compressor. I also checked and the freon is full.
The plug to the compressor also has a diode from the hot side looping over to the ground side. Is this normal ? (I have never seen that before).
All help is appriciated.
Thanks

1 Reply

RASMATAZ

MECHANIC
75,992 POSTS

One of the first things you should check, therefore, is compressor engagement. If the compressors magnetic clutch is not engaging when the A/C is turned on, the problem may be a blown fuse or a wiring problem. If the fuse is blown, replacing it may restore cooling temporarily. But the underlying reason for the fuse blowing in the first place needs to be identified and corrected to prevent the same thing from happening again.

If the magnetic clutch is receiving voltage but is not engaging the compressor, the clutch is defective and needs to be replaced. If there is any evidence of leakage around the compressor shaft seal, the seal should also be replaced.

If the clutch works but fails to turn the compressor (the belt may squeal in protest!), The compressor has seized and needs to be replaced.

Compressor failures are usually the result of loss of lubrication, which in turn may be due to low refrigerant in the system, a blockage (such as a plugged orifice tube which prevents refrigerant and oil from circulating to the compressor), loss of lubricant due to leaks or improper service procedures (not adding oil to the system to compensate for oil lost through leakage or component replacement), or use of the wrong type of lubricant.

R-12 systems require mineral oil while R-134a systems require various types of PAG oil or POE oil. Using mineral oil in a newer R-134a system can cause serious lubrication problems as can using the wrong grade (viscosity) of PAG oil. Always follow the vehicle or lubricant manufacturers compressor oil recommendations.

The next thing you should check when troubleshooting a no cooling problem is system pressure. For this, you need a set of A/C service gauges. Attach your service gauges to the high and low service fittings. If both the high and low side pressure gauges read low, the system is low and needs recharging. But before any refrigerant is added, check for leaks to find out where the refrigerant is going.