1999 Chevy Cavalier A/C Compressor

  • 4 CYL
  • FWD
  • 140,000 MILES
We have owned this car since new and have meticously taken care of it. The A/C has always blown very cold. On a hot, humid Saturday we left our house. Driving at 40-50 MPH the A/C was cold as usual. However, as soon as we hit a red light and stopped, the A/C rapidly warmed up and actually blew rather hot air. The rest of our short trip was the same - when the car was moving, the A/C was cold, but in traffic or at a light it was hot air. I noticed the car (radiator) temperature guage was going up on the way home. At home, I lifted up the hood and almost burnt my hand of the stick to hold open the hood - clearly the temp guage was correct. I thought maybe the A/C Compressor, so I started the car with the A/C off. The pulling were turning and everything seemed fine. I turned the A/C and clutch engaged and everything was turning, but the engine appeared to be lugging - like pulling a heavy trailer. We turned the A/C off and took the car for a ride. It ran fine. The radiator temperature guage went back to the middle, where it always was.

Given these symptoms, it seems like the A/C compressor is about to seize. Is that correct? Will the car continue to operate fine if we leave the A/C off? If it is the compressor (or whatever the problem), how big a job is the repair and can I do it myself? I've changed water pumps, brakes, brake calipers, alternators, stuff like that.

Look forward to your guidance!
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have the same problem?
Monday, July 27th, 2009 AT 8:30 PM

1 Reply

An A/C system that blows cold air for awhile then warm air is probably freezing up. This can be caused by air and moisture in the system that allows ice to form and block the orifice tube.

Evacuating the system with a vacuum pump will purge it of unwanted air and moisture. Evacuation should be done with a vacuum pump that is capable of achieving and holding a high vacuum (29 inches) for at least 30 to 45 minutes.

For best performance, an A/C system should contain less than 2% air by weight. For every 1% increase in the amount of air that displaces refrigerant in the system, there will be a corresponding drop of about one degree in cooling performance. More than 6% air can cause a very noticeable drop in cooling performance, and possibly cause evaporator freeze-up.

Air can get inside a system through leaks, by not evacuating the system prior to recharging it, and/or by recharging the system with refrigerant that is contaminated with air. Recovery equipment can suck air into the recycling tank if an A/C system contains air or if the system has a leak. For this reason, the refrigerant recovery tank on recycling equipment must be checked and purged daily. On some equipment, this is done automatically. But on equipment that lacks an automatic purge cycle, tank pressure and temperature has to be measured and compared to a static pressure reference chart.

Some refrigerant identifier equipment can detect air in the system as well as other contaminants. An identifier should be used to check the refrigerant before the system is serviced to prevent cross-contamination of recovery and recycling equipment.

Possible causes of intermittent cooling in a manual A/C system that might be caused by an electrical problem include:

Faulty low pressure cutout switch. This switch prevents the compressor from running if the refrigerant level is low. If the cutout switch is not reading correctly, it can prevent the compressor from coming on.

Faulty compressor clutch. The magnetic clutch on the compressor requires full battery voltage to engage. If the voltage to the clutch is low, or the clutch coils have too much resistance, or the air gap in the clutch is too great, the clutch may not engage to drive the compressor.

Faulty compressor clutch relay. Check to see if the relay is receiving voltage when the A/C is turned on. Also check the relay wiring and ground connections. If bypassing the relay with a jumper wire or routing battery voltage directly to the compressor clutch makes the A/C work, the relay is probably bad.

Faulty A/C control switch. The switch may be worn and not making good contact when it is turned on.

Some possible causes of intermittent cooling (or no cooling) on automatic A/C systems include all of the above, plus:

A problem in the control module or control head (this usually requires using a dealer scan tool to read fault codes and perform self-diagnostics).

A bad temperature sensor (an ambient air temperature sensor, interior air temperature sensor, evaporator temperature sensor, or sunload sensor). Again, a factory scan tool is usually required to perform diagnostics on the system.
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Monday, July 27th, 2009 AT 8:35 PM

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