Need help diagnosing BMW AC problem

I need to tap into the GRM brain trust for help with a vexing AC problem with my E39 528i. It has been in for repair several times for this problem with the mechanics "guessing" at my expense to the tune of over $1400 without solving the problem.

Here is the deal: The AC works just fine. Nice and cold. When it wants to.

It never works when the car is first started for the day. If the car has been driven for 20 minutes or so and then restarted, it usually comes on. Takes longer on hotter days (of course). Once it does start working it will work well until the car interior is cooled off and when it starts to cycle to maintain temp, it stops cooling completely. Turning the AC button on the panel off and on resets it and it will start cooling again. It can be made to stay on longer if the fan speed is turned from auto to manual and set at a high speed.

I know that it is nothing mechanical because I have already paid to have the compressor, dryer, etc. changed. The shop wants to take the dash apart and replace the flaps that direct air cool/warm dash/vents etc. They want $800 for this guess. I am not too enthusiastic about letting them try. My thought is that I could get a replacement dual zone climate control panel off of eBay and change all the dashboard electronics.

Anybody have any knowledge about this stuff?

Hmmm. Swing and a miss. Nobody with any thoughts? Not even the BMW bashers telling me I should have bought a Honda, etc.

Try over on the Bimmerforums General Mechanical forum; that's where all the pro techs hang out.

Had a similar problem on my e36 m3. Turns out a capacitor goes bad on the circuit board in the AC controller. Not sure if the 5 series shares the same problem, but they are from the same era. Here is a problem for the fix if that is it.

http://www.macadamizer.com/bmwfix.html

Again, I would check to see if other people have had the problem with an e39