Air conditioning causes idle problems

[Stuartino]

Hi all, I have searched without much success for a solution to this, maybe I am using the wrong words.
I have a 1998 E36 M52 323i auto. I bought it two years ago, the AC worked fine then. The problem is that when I try to use the air-conditioning, the cars performance is terrible, the revs drop or stick, or even race. The car feels like it is going to break down at any moment. The last time it was like the cruise control was stuck on, which it wasn’t, without needing to press the accelerator the car kept the revs up and seemed quite happy doing so, with a couple of rev dropping moments.
I have tried cleaning out the idle control valve. After doing that the car behaved in similar way for about a 50 miles on the motorway, my understanding is that the ECU recalibrates? I think when you engage the AC an extra belt engages the timing belt, this feels like it is slowing down the engine. If I don’t use the AC, the car is absolutely fine. No problems at all. As I live in the UK, it not often you have to worry about the AC, its rarely warm enough! But summer is coming and for the few days that I will need it, I would like to think I can.

[Big Evil]

Sounds like you have an a/c compressor getting ready to explode. The ECU raises the idle when the compressor is commanded on and responds to keep the engine from bogging down. If the a/c charge is low, the compressor can switch on and off causing the idle problem you're describing. The other possibility is overcharge which can result in the compressor sucking in liquid refrigerant and stopping momentarily or just blowing the compressor case wide open (seen it, it's awesome when some bonehead does it). I'd get it in and have the charge level checked and get the system leak tested. I also wouldn't try using the a/c until you do so, the refrigerant is a system lubrication (mixed with PAG oil) and low charge can lead to premature failure of the bearings/seals in the compressor.

[Stuartino]

Thanks Big Evil. When I bought the car I had it refilled, but all cars overall certain age leak AC. A friend of mine who does main dealer all the way, spent a lot of money trying to find the cause and stop his AC from leaking. In the end he was told it was cheaper to refill each year. I have had a lot of radiator and heating problems, so I have lost count of the number of times the radiator has been out, which means constantly knocking the AC pipes, which is probably not ideal.