A/C only works when it's cold outside

[CorvallisBMW]

So I have this very weird problem: My A/C is fully charged, with a new receiver/drier and new evaporator. It runs great when the temps outside are below 70 degrees, but above that the A/C cuts out almost constantly and the clutch spends almost no time engaged. I tried testing the pressure sensors on the receiver/drier while it was doing it's funky on/off bit, and I saw no voltage change at all. I got the same results when i tested the small single wire sensor on the compressor. Any ideas as to what could cause the A/C to cycle off so much?

[backtrail69]

I wonder if the electric clutch on the compressor is bad/weak??

[RobertK]

Sounds like it might be over or under pressurized.

[CorvallisBMW]

Sounds like it might be over or under pressurized.

That's what I though too, but the sensors appeared to be working fine and they were not switching open or closed when I tested the voltage across them.

[jlevie]

Check to see if the aux fan is operating. With the car stationary or moving slowly an in-op aux fan will cause a high pressure cutoff.

[bala_eos]

My guess is aux fan resistor.

[CorvallisBMW]

I did some more looking in to it, tried bridging all the wires going to the various sensors. If I bridge the low pressure sensor on the r/d it seems to run ok, so I'm guessing that's where the problem is. I am going to try filling it with a bit more R12 and see if that helps.

[z3pilot99]

I have been working on my AC too. I think I am done with it. It doesn't cool like I think it should. I get 49 degrees output when going down the road at 50 mph & 90 degrees outside (R-134a, new compressor, receiver/drier, expansion valve and all new O-rings). I think I am going to flush the entire system and refill again. I didn't do it the first time. Anyway, I found a forum that is very helpful. http://acsource.net/acforum/