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Old 25th June 2011, 22:03   #1
kevin711
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Air conditioning troubleshooting

So I went to use my AC today and it wasn't blowing cold. I ran the AC once in awhile in the winter/spring when it was above 5 degrees C or so and I thought it worked since the compressor worked. I did a search and went through every thread here and on bimmerforums, and here's my findings so far:

- All hvac fan speeds work, and all vents blow the same temperature roughly -- likely not the fsu
- when I turn the center vent wheel from 3 blue dots into the red, I get heat... so the flaps seem to be working
- when I change the vent options (feet well, center, windshield) all of them work as well
- the AC light turns on when the snowflake is pressed

- the outdoor temperature sensor works ok, it reads the correct outdoor ambient temperature

- my front auxiliary fan is working, it spins up and down at idle (it spins pretty fast and loud sometimes)
- the AC compressor clutch engages -- I can see it spin with I turn on the AC and I can hear the compressor click in
- i used a low pressure AC gauge and with the AC off, it reads 45 psi ,with the AC running it reads 32-33 psi

- I checked the plug on the evap canister and it is getting power (approx 5v on two lines) and has ground
- water valve under the hood on the driver side is getting power


am I low on r134 or should I look at something else?
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Old 25th June 2011, 22:05   #2
dan.
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i had a similar issue but turned out to be the hedgehog was messing about for the second time.
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Old 27th June 2011, 00:29   #3
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alright, I'll order one of those FSU's... not sure when it was last replaced and it's cheap. Worth a shot.
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Old 27th June 2011, 03:16   #4
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Quote:
Originally Posted by kevin711 View Post
- i used a low pressure AC gauge and with the AC off, it reads 45 psi ,with the AC running it reads 32-33 psi
You're most likely low on charge as the high and low sides should equalize at a higher pressure with the compressor off. The weakest point of the system is the service port valves and we replace them on a very regular basis.

I'd recommend having the system evacuated, valves replaced, and then re-charged with some dye. From there you can start looking for other leaks.

The FSU only controls fan speed and if you are able to address multiple fan speeds and they are stable then the FSU likely isn't an issue here. There could be some issues with the controller or the mix door in the airbox, but at this point the pressures don't look right so I'd start there.
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Old 1st July 2011, 05:54   #5
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I brought the car to an AC shop, they tested for leaks and existing pressure, everything looked ok.

They evacuated the system and refilled it with fresh R134A, lube and UV dye and it works fine now. The tech said likely the old refrigerant was dirty (contaminated)...
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