air con problems - saga continues

Hi All
2001 530i sport, UK spec
I have tried posting this twice from oe6 but it didn't appear to appear (I think thats what I mean), therefore I am posting via google......
Some time ago I posted my problem re air con which I then joyously announced I had fixed - how wrong could I be!!!
Just to recall - I have my air con on auto, at 16C both sides of the cabin. At what now seems random times, the blowers in the foot wells and the windscreen will blow hot air (and I mean hot, hot, hot) whilst the dash blowers continue to blow chilly arctic winds. Obviously, a temporary solution is simply to have only the dash blowers on, therefore ensuring chilliness. Having gleaned information from the web, this NG and various mechanic-oriented friends, I thought the problem might be that the air con needed checking, re-gassing, etc.
Had it checked over and re-gassed which results in things getting cooler quicker; however, since, I have experienced hot feet + screen on two occasions. I can simply switch off the ignition for 20 mins or so and I get cold air again - though not always, sometimes it persists all day, sometimes not (awkward, ain't I?). The only other thing that needs fixing is the condenser fan which I have been told needs overhauling 'cos it ain't working.
Does this ring bells with anyone?? Will having the condensor fan fixed make things better?? If it helps I did replace the 'final stage resistor' a few months back as all the blowers had stopped - could this be faulty; does it have anything to do with the blowers blowing hot or cold???
Sorry, lots of questions, but I'd appreciate all constructive advice (even if someone 'knows' that the fix could cost squillions - I'd just like to know whats wrong). If worst comes to the worst, I'll simply continue using the dash blowers when the problem occurs but I really would like some idea as what is happening.
thx
Jon Manley
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The problem is NOT with the air con. You are getting hot air because of the heater. If the hot air came out all the time, I would think the heater control valve was stuck open. But this sounds like a control problem. Something is telling the heater valve to open. That would probably be something in the control panel. Another possibility would be a wiring fault.
This is not very specific since some good diagnostics have to be performed. But it will send you in the right direction.
Bob
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Bob Smitter wrote:

I don't know about BMWs, but US cars typically use vacuum to operate the mixer valve in the plenum. If there is a vacuum leak, you get just this sort of behavior. It usually happens when you dip into the throttle, thus lowering engine vacuum, for a longer period of time. Once the vacuum reserve is used up, vacuum is insufficient to hold the valve in the "cool" position, so it tries to revert back to it's relaxed state, which is full hot.
Vac leak could be in the control switch, in vacuum lines, on the engine, under the dash, or it could be a bad diaphragm in the vacuum pot that physically moves the valve. If the car runs and idles OK, I'd suspect something in the dash first, although the fuel management can compensate for some leakage.
Lots of assumptions here, so I could be way off base per your problem.
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The fresh air vents aren't fed in the same way as the screen and foot ones - as you'll have noticed there is a separate temperature control for them. So I'd guess the hot/cold air blending isn't working correctly on the main system. My guess is a stuck or faulty motor - but not sure where it is.

The aux fan improves the efficiency of the AC at low speeds - but won't make any real difference to your problem.

That's a common fault on the E39 and again not related to your current problem.

There is a specialist E39 e-mail group with lots of expertise, and you may find someone who knows the exact answer. The address is in my sig below.
--
*Real women don't have hot flashes, they have power surges.

Dave Plowman snipped-for-privacy@davesound.co.uk
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Same thing happened to my E39 535i (well, nearly - I was getting continuous hot air on feet/screen) - a/c control panel needed replacing. Part costs 348 + VAT + 95 for commissioning by BMW (apparently it needs some programming/setting) + ~30 minutes of time to replace. Total 600+...
There are people that claim they can repair the part, but I haven't found one that actually could. In July's BMW Car Magazine (in WH Smith now) there is an address of a North-London based repair shop - sorry, but I left the magazine in the plane.
Hope this helps. Good luck
Davide
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snipped-for-privacy@hotmail.com wrote:

I strongly suspect this is the case, although mine is intermittent at the moment. Now all I need to do is find out if it can be repaired or replaced (fairly easily) with a unit from a breakers, maybe.
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