A/C not working, but aux fan does...

Hi, I'm new to the BMW scene and have been trying to do some research on my problem. I recently acquired my first BMW. It is a 1999 540i/6 Sport with 104,000 miles. I got an awesome deal on it as everything is in mint condition but the A/C is not working. I would really hate for this to bring down my first impression of BMW ownership. I have read that some people say the the A/C won't come on if the aux fan isn't working, but that's the thing. I can hear the aux fan start when I first start the car (loud jet noise that stops after a few moments) but my A/C still blows warm air. The temp sensor seems to still be working as I have an accurate ambient temp reading. The aux fan also turns on when I start the car and I believe it does while I'm in traffic, but I don't believe it comes on when I turn on the A/C. Any help would be greatly, immensely appreciated!

P.S. Sorry about the huge block of text, I just would rather provide more info than less. Thanks!

The only thing you didn't provide is MY, build date, and mileage.

Does the compressor clutch engage when you turn on the A/C? If so, the system may have a leak, and the refrigerant is gone. If it does not, there is a fault in the IHKA (aka HVAC control). This will require a diagnostic vie BMW DIS.

If the compressor does not kick on, there may by a blown fuse. Are you determined to troubleshoot this yourself? If so, buy a copy of the Bentley E39 service manual.

I read that the A/C clutch is supposed to "click" when it engages, but I do not hear anything. I have checked the fuses and they seem to check out. I want to troubleshoot it myself but was just looking for some helpful tips...

Also look at your RPM needle when you turn on and off the AC, you should see a bump in the needle if the compressor kicks on while in park.

Yeah, while the car is in neutral and handbrake is on, the idle stays the same...it's almost like absolutely nothing happens. I think that the a/c clutch isn't engaging...

When you press the A/C button, the IHKA panel sends a request to the DME to increase idle speed. Once acknowledged, the panel then energizes the clutch. As I mentioned, this may require diagnosis via DIS.

I apologize: I obviously did not read you post carefully!

Bummer, no AC just in time for summer. I hope it's something cheaper then a new compressor.

edjack-what? I don't get what you are saying...are you stating that I should get a reader and see the the ecu throws a code? please elaborate...
bcbp14-yes, it sucks. Yesterday was 90 degrees and the black leather was hot enough to fry and egg...

Hey dude check this site coz i do have that problem.... And wahhlaaaa it's like magic ,,,, and cold air is pumping like Alaska.....http://tis.spaghetticoder.org/s/view.pl?1/06/04/47

cbruce2012,

Carefully read my post. It is clear to me, although I'm the one how wrote it! The HVAC needs to be diagnosed via the BMW DIS computer, unless the evap temp sensor replacement solves the problem, as izrahel indicates.

UPDATE: The loud whine at start up was actually cause by my failing SAP :/ The AUX fan does work though because I noticed it turning on in traffic the other day while it was 95 out. I think I am going to take it in and have the A/C looked at. I will let everyone know what the cause of the problem is and how much it was to repair. BTW, is there a thread regarding the average price for e39 repairs?

I got the A/C checked at a shop and they said that it was leaking at the dryer and the pressure switch. They want $150 for parts and $250 for labor, so I think that I'm just going to buy the parts and install myself...
If there is any interest, I'll make a DIY for others...

Congrats on getting the A/C system diagnosed. Replacement of the parts mentioned should be fairly straight forward.

My question is, do you have the vacuum pump needed to evacuate the A/C system after you replace the parts? The system will be open to the atmosphere and therefore moisture will have entered it. This moisture needs to be removed. If not and you just add refrigerant, the compressor will have a very short life. A/C compressors can't compress moisture and quickly break when forced to.

Also do you have the knowledge to fill the system to the correct operating pressures? BMWs have specific needs in that regard-too much or too little refrigerant will yield no cooling. If your shop's price included parts, install, evacuation and recharge, you are getting a deal.

Just trying to be helpful

Not sure why nobody mentioned this but common AC culprit is failing final stage resistor unit. They all go bad and result in a system with odd behavior: blowing hot air, fan working sporadically or not at all, only on low speed, etc.

This is the cheapest thing in the AC system to fix and takes 10 minutes. Search for FSU and you will see. I would replace it before throwing hundreds of dollars at this problem unless there is a visible leak that they pointed out to you.

Johnstern- I though I would just have to replace parts and charge the system, but maybe now I'll just have them do it.
Joshp-he said the minute he did a leak test(the system had no charge) he was able to see it leaking from the specified area, and except for being warm, my climate works fine, hence my assumption on the a/c system itself.

johnstern is correct about evacuating the system before you add refrigerant. Typically, they replace the components, add oil if necessary and apply a very strong vacuum for 30 minutes or more then check for leaks afterwards. If the vacuum holds, then you charge the system by weight.

IIRC, water in the system reacts with the PAG oil to form an acid. The vacuum lowers the pressure enough that the water in the system vaporizes.