[mrvedit]

On the 2011 535i we just bought, the A/C cycles on and off every minute which prevents optimal cooling.
With engine running and A/C controls set to lowest temp, I put a pressure gauge on the low pressure side and it alternates from 25psi to 50 psi as the compressor cycles on and off. Its about 30 seconds on, then 30 seconds off. I tried different A/C settings, such as Max with re-circulation and just regular; it doesn't make much difference.
While not an A/C expert, the pressure indicates there is enough charge and the interior vent air temp of 40F when the compressor is running indicates it is mechanically sound.

Any ideas? Is there a possible pressure sensor malfunction? Hoping its not an A/C control unit.

My daughter has this car in Colorado - I'm just trying to give her some guidance. She will likely take it to an independent shop based on what you guys think.

Thanks.

[chipguy]

Originally Posted by mrvedit

On the 2011 535i we just bought, the A/C cycles on and off every minute which prevents optimal cooling.
With engine running and A/C controls set to lowest temp, I put a pressure gauge on the low pressure side and it alternates from 25psi to 50 psi as the compressor cycles on and off. Its about 30 seconds on, then 30 seconds off. I tried different A/C settings, such as Max with re-circulation and just regular; it doesn't make much difference.
While not an A/C expert, the pressure indicates there is enough charge and the interior vent air temp of 40F when the compressor is running indicates it is mechanically sound.

Any ideas? Is there a possible pressure sensor malfunction? Hoping its not an A/C control unit.

My daughter has this car in Colorado - I'm just trying to give her some guidance. She will likely take it to an independent shop based on what you guys think.

Thanks.

You might actually have too much R134a in the system. If this is true, the high side pressure will be too high and the system will stop the compressor. Was there work done on the A/C? If so, who was doing it?

[mrvedit]

Since the low side pressure goes up to 50 psi I also wonder if there is too much R134. We bought the car over the winter and the A/C was not tested until recent hot days in Denver. No idea of any work done before we bought it; I did have a PPI done.
Thanks.

[SWFLf10]

I've heard of the ambient air temperature sensor failing and causing the car to think it's too cold outside for the ac to safely run. Hopefully it's something as simple as that.

If at all possible try to read any codes present using ISTA.

[chipguy]

Originally Posted by SWFLf10

I've heard of the ambient air temperature sensor failing and causing the car to think it's too cold outside for the ac to safely run. Hopefully it's something as simple as that.

If at all possible try to read any codes present using ISTA.

If it is the ambient temp sensor, the compressor will not be cycling on and off. You should check the high side pressure, this is a much better indication if the system is over charged. Of course, the most accurate method is to evacuate and find out the weight of the R134a in the system.

[mrvedit]

Originally Posted by chipguy

If it is the ambient temp sensor, the compressor will not be cycling on and off. You should check the high side pressure, this is a much better indication if the system is over charged. Of course, the most accurate method is to evacuate and find out the weight of the R134a in the system.

Agreed. While my shops have R134R and 1234YF equipment, I didn't think to check it when the car was in Michigan. I'll just suggest she have the system evacuated and re-filled correctly. (She is in Denver.)

I just wondered if this was a common/known problem due to a faulty sensor or setting.
Please consider this thread closed unless I open it again if a re-charge doesn't fix it.
Thanks.

[chipguy]

I am not aware of common issues with sensors on this car. The most common problem I heard is leak in the condenser. But that does not sound like your problem.