Air condition compressor always on?

[yiannosk2]

I had a compressor failure and I took it to a techninial to replace it. After replacement he did some tests and he said that maybe something is wrong. Whatever temperature he set, the compressor is running nonestop for hours, until you manually sitch it off.

Is this normal?

[RFM]

Certainly not on AC systems with a compressor equipped with an electromagnetic clutch (986/996/987/997), unless you are at the equator, the temp. set to LOW and the convertible top is open. The system will clearly need to be further investigated if this is not the case.

[yiannosk2]

I have visit my mechanic just to check it with the PST diagnostic. NO ERRORS at all. Nobody knows where the problem is....

Any suggestions? You are my last hope guys! :help:

Edited January 28, 2011 by yiannosk2

[RFM]

Is the correct fill level held? With for example 200 gram too little, he will still function but should be circulated more to maintain an acceptable cooling capacity. PST and PIWIS diagnose not everything, i would advise you to contact a AC specialist or a experienced dealership.

[yiannosk2]

He added 850g refrigant and 210g PAG 46 oil. He put a thermostat on the vents and it was blowing air 2 C while the ampient temperture was 18 C.

The only thing that I suspect now is the climate control unit... :(

[yiannosk2]

Loren? Any experience with something similar. Because I don't want to start buying parts to find the problem ;)

[Loren]

I agree with RFM - find an AC specialist. Tell them you have already spent a lot of time and money and want a solution.

[whall]

Perhaps I haven't read the problem correctly but, doesn't the A/C compressor run continuously with the HVAC "ON" (in AUTO) if the ambient temperature is higher than 32 degrees F/0 degrees C?

Bill

[wwest]

Perhaps I haven't read the problem correctly but, doesn't the A/C compressor run continuously with the HVAC "ON" (in AUTO) if the ambient temperature is higher than 32 degrees F/0 degrees C?

Bill

No.

The compressor shuts off if:

The high side refrigerant pressure becomes too high or too low.

WOT.

The engine coolant "threatens" to rise too high.

The cabin atmosphere reaches or is below the setpoint.

OAT is below ~35F

Evaporator surface temperature, close downstream airflow, is below 33F for more than 2 minutes.

[whall]

wwest,

Thanks for the information. Things can get pretty complicated quickly when trying to troubleshoot problems.

What things will make the A/C compressor stay "on" in the AUTO mode, which I believe is the problem stated in this thread?

Thanks,

Bill

[mdgcentral99]

Actually, I read that the compressor stays on unless ambient is below 35 degrees. It has to do with removing humidity from the air so the windows wouldn't fog up and the cabin doesn't become too sticky. It then adds heat to keep the temperature comfortable. But the compressor stays on. I'm pretty sure, but I'm no mechanic. Maybe earlier models are different, but mine is a 996.

[RatboneRanch]

Actually, I read that the compressor stays on unless ambient is below 35 degrees. It has to do with removing humidity from the air so the windows wouldn't fog up and the cabin doesn't become too sticky. It then adds heat to keep the temperature comfortable. But the compressor stays on. I'm pretty sure, but I'm no mechanic. Maybe earlier models are different, but mine is a 996.

+1. Practically every car made in the last 10-15 years with auto climate control seems to keep its AC on all the time unless you override it manually.