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Discussion Starter · #1 ·
Hey everyone!

I'm desperately in need of some help.. I purchased a 2002 525i about a year ago, the freon just went out a couple months ago.
Being the "handy man" my husband is, we made the mistake of putting in "A/C Pro Ultra Synthetic R-134 Refrigerant". The AC worked GREAT for a couple days, then out of nowhere, nothing but hot air.

I looked everywhere to figure out the problem, and found the AUX fan wasn't spinning. I changed the AC temp sensor thinking it might be that-- nope.
The fan isn't locked up (spins easily when manually rotated.. if that makes sense).

I'm waiting to take the car into the mechanic shop to figure it out, but that isnt until a couple weeks. I'm located in South Texas, so the heat down here is pretty much unbearable.

Any help, suggestions on where to look at, or personal experiences y'all have had would be greatly appreciated.

Thanks in advance!! :)

· Registered
2003 530i
2,292 Posts
Given your description, a refrigerant leak is a real possibility. On your 2002, the HVAC panel monitors A/C pressure and it it's too low will refuse to try to start the A/C compressor. If this is so, the aux fan will not be started either: the aux fan isn't started until A/C pressure rises to 5 bar (~70 psi), i.e. after the compressor has started working.

Your 2002 will have the pulse width modulate (PWM) aux fan whose speed is controlled by the engine controller. These fans do fail- I'm on my 3rd in 11 years of ownership. Some E39s with the PWM fan won't even try to activate A/C if the fan is bad, others will, and there seems to be no way to predict which car will do which. (I'm in the category of inop aux fan = no A/C) However, when the engine is started, the engine controller (DME in BMW speak) runs the fan for a split second to check it's OK. So you & your husband could check that yourselves. The acid test for the fan is a scan of the DME for error codes. A faulty fan shows up as a BMW fault code 125; there is no Pxxx style DTC for a faulty fan so a generic OBD scanner may not report a faulty aux fan.

As, or if, you're reading other threads about A/C problems, beware that earlier E39s used a 3 stage aux fan using relays and resistors. The A/C and aux fan control strategies are entirely different. For instance, with those cars, the aux fan is started at the same instant that the HVAC panel tries to start the A/C compressor, quite different from your PWM fan.

For many A/C problems on your 2002, the mechanic will need to have a diagnostic scanner able to read several of the cars modules. A generic scanner won't do that - engine and transmission only. So ask if they have some familiarity with E39s, &/or documentation that will step them through the system.

BTW, welcome to this forum. And I'll cross my fingers for cooler weather until you get your A/C working.

EDIT: I just noticed you're expecting to wait 2 week to see a mechanic - perhaps for a BMW specialist. That's a long time to drive a sauna car. I should have mentioned that you do not need a BMW specialist for A/C repair. But whoever you go to does need to have access to BMW data and a diagnostic scanner able to read the entire car.

EDIT2: on second (or third?) thought there are some thing that could be done by any old auto A/C shop without BMW data or scanner. First would be to jumper the A/C compressor clutch to see if it engages - if not the clutch or entire compressor needs replacement. If it does engage, does it make any cold air? Second would be to search for a refrigerant leak. They would add a little R134a and look for a leak. Some will add dye to the R134a and then use a UV light to see the leak after a few hours running. Better shops will use an R134a sniffer that will detect the escaping refrigerant immediately after adding the refrigerant. I think if that doesn't find the cause, you'll have to find someone BMW equipped.
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