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ac compressor doesn't switch on- What could it be?

568129 on Sun December 25, 2011 11:03 AM User is offline

Year: 2002
Make: Bmw
Model: 530d
Engine Size: 3000
Refrigerant Type: r-134
Ambient Temp: 79 f
Country of Origin: Nicaragua


The ac compressor doesn't switch on when I turn the ac on. I checked the fuses for the air conditioning and they are fine. How can I fix this problem? Is there a switch for the ac compressor that I am missing here. The ac system is loaded with freeon and has correct pressure just that when you turn on the ac all you get is warm air because the ac compressor doesn't switch on. I really appreciate the help.We checked the ac compressor for pressure and got 100 pounds meaning it has good pressure so that isn't the problem.The fuses for the ac look good.

There is a black cable that goes to the top of the compressor and I checked for voltage while the car was running and got nothing. Is this the cable that turns on the compressor clutch? If so then the compressor clutch would be getting zero voltage. Why would that be?

Any help is appreciated. Thanks

NickD on Tue December 27, 2011 7:59 AM User is offline

A hundred psi of static pressure doesn't mean a darn thing, can get that with just a few ounces of R-134a in a system. After a careful leakage test and checks for any oil drips, I use a variable DC power supply to directly energize the compressor directly to make sure refrigerant is not the problem. With an ammeter on it, tells me the clutch current that should go down a tad as the coil heats up. Also the clutch pull in voltage, normally around 10 VDC. Also assures me the clutch gap is correct by rapidly pulling in. Excessive clutch gap can also be your problem.

This bypasses all the electronics and assures me the system is correct by observing operating pressures. Doesn't take that long and lead the problem to the control system.

Does this car have automatic climate control? Anything wrong with that will prevent the compressor from engaging, like an open ambient or in-car sensor. Would never attempt this without a circuit diagram and even learn if the system generates error codes to help isolate the problem. Can also end up pulling out the rest of your hair.

Dougflas on Tue December 27, 2011 5:00 PM User is offline

Nick is exactly correct. You should invest $25. to $30.00 and purchase the All Data cd for this vehicle. This way, you'll be able to troubleshoot correctly.

mk378 on Tue December 27, 2011 9:21 PM User is offline

Yes you'll need a schematic, etc. If the car is not delivering voltage to the compressor clutch even though there is pressure in the system, it's an electrical problem.

568129 on Thu December 29, 2011 3:14 PM User is offline

Ac is manual not automatic funny thing happened now the compressor started working again what could make the compressor work intermittently ?

GM Tech on Thu December 29, 2011 6:27 PM User is offline

cold weather.......the a/c system will work depending on pressures and temperatures-- if too cold- no a/c

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

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