JasonF

My engine will vibrate as I pull through 3,500 rpm's and continue through 4,500 rpm's only when the air conditioning is on. Seconds later, when I accelerate through the same range with the A/C off, the car runs just fine.

It has been quite hot in the Northeast and the temperature coming out of the center vent was 45 degrees while the car was sitting in my 100-degree garage with the engine nice and hot...so the a/c seems to work just fine

Tips from Rennlister's who have experience with the problem?

Thanks!

TamiyaGuy

Sounds like it might be the belt or gear on the condenser. Can you look at the engine while someone else revs to 3500 with the AC on? If you can feel the vibrations, it might be obvious to a visual inspection.

993Maineiac

Also you might check the brackets-unlikely but you could be getting a sympathetic vibration if one is cracked.

Al

rockdoc

I actually get noticeable decrease in performance when the airconditioner is on. Do others get that?

JasonF

Definitely. In fact, I find myself driving with the windows down in the 90-degree heat (sometimes) rather than live with the sluggish-feeling engine when the a/c is on.

willisit

I had the same problem.. one of the bolts holding the compressor had come loose (the nut was missing completely!)... after a service. Hmm.. anyways, I bolted it back on and the noise subsided. While it was loose the car didn't perform and was noisy... check it out - you'd not imagine one bolt making such a difference!

JasonF

Thanks Dan! I'm also noticing a degradation in performance only when the a/c is on (as mentioned above)...all cars I've ever owned aren't as peppy when the a/c is blasting, but my 993 takes it to a new level.