Starting A/C kills engine
 

Hi, after years of dreaming, I'm finally a Porsche owner with a '78 911SC. 70K original miles and in excellent condition cosmetically and mechanically. So far I'm very happy with the care put into it by the previous owner. When I purchased the car just a few weeks ago, the A/C system had just been completely "redone". However, anytime I try to crank on the system, the engine dies. It seems like the idle boost is not sufficient to sustain the system. If I let the RPMs down easy, it seems to "hold on" and the system remains running but if I tap the gas, RPMs drop hard and engine dies... again, only when the A/C is on. I've been asking around and tinkering but can't seem to figure out what types of adjustments (if any) I can make to adjust the idle boost. Any suggestions would be greatly appreciated! For what it's worth, I had a friend/mechanic (unfortunately not a Porsche expert) check the refrigerant and he said it looks fine. Frankly, I've never had the A/C running long enough yet to see if it will really get cold. Mildly cool is about as close as I've gotten.

Could be that there is too much freon in the system. The original York compressor is notorious for taxing the engine at idle compare with a more modern compressor such as a sanden or a seiko seiki.

There isn't an idle boost circuit for the air conditioner. What is the idle speed of your car with the a/c off? Perhaps a simple increase in your idle speed adjustment is all that is necessary. I set mine to 1100rpm during the summer to compensate for the increased pull of the compressor and to promote more airflow across the condensor when the car is at a stop.

You also may be running a bit rich in mixture.

Thanks for the input guys! I let a little bit of freon out and also found that I had a small air leak at the base of the hoses behind the airbox housing... snugging these up seems to have helped a little. I also increased idle speed to right at 1000 and that helps a bit too. All in all, the compressor is still killing the engine when I let off the accelerator quickly. I'll try to do a little more tweaking and see how I come out. Again, thanks to everyone for their suggestions!

'78SC Silver Coupe

I do what Motorhead does and it solved the same problem with my SC.