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Strange pressure readings

dhaz0221 on Mon August 30, 2010 12:30 AM User is offline

Year: 1999
Make: BMW
Model: M3
Engine Size: 3.2
Refrigerant Type: R134A
Ambient Temp: 105
Pressure Low: 30
Pressure High: 240
Country of Origin: United States

I am having an issues with the pressures on my BMW M3 at idle the low side is 30 and the high is 240 at 105 degrees ambient. This seems normal however if I rev the engine to 1,500 rpms the low drops to 18 and the high goes to 310. My problem is excessive cycling while driving down the road and this weekend I drove up to the mountains (lower temp) and the evaporator froze up. First I thought thought a low charge (thus the low side being so low) but the high side seems normal. I am wondering if I now have a restriction at the expansion valve causing the excessive low side.

BTW---readings where taken with fan speed on high-doors and windows closed and on recirculate.

Vent temps are 32-34 degrees but you can definately tell it is cycling alot because you can feel the vent get REALLY cold and this warm and then REALLY cold again.

Any thoughts?

1stbscout on Mon August 30, 2010 1:25 AM User is offlineView users profile

It sounds like you may have a problem with the TXV. Then again if the evap froze up your low side control is not working properly either as it should not allow the low side to get low enough to freeze up the core. The low side control should shut the compressor off at roughly 26 psi no matter what the rest of the system is doing.

Edited: Mon August 30, 2010 at 8:30 AM by 1stbscout

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