I have a '94 c280 and the center A/C vents turn themselves off on acceleration (come back on when you let off), there is an audible vacuum (noise) coming from within the dash (high pitched squeal also changes with accereration). I have tried to determine the problem and was told there is a "one way vacuum valve" but I cannot find it. Can someone please advise me if this info is correct and/or where to find the valve or what else to look for?

Thanks,
Gary

 

The A/C compressor disengages when you accelerate at or near full throttle. It gives you back the hp you need that you lost by having the A/C turned on. The vacuum noise is probably normal. Hard to tell without hearing it. A high-pitched squeal doesn't sound normal, but I don't know what it would be.

 

lugnut....

I'm sorry for omitting some additional info re: this problem:

I have a number of years under my belt as a mechanic/service manager for a few different brands of autos.

I do have a vacuum leak.

I am looking for someone to tell me where to locate this supposed "one way vacuum valve" (where on the car).

The car dies at idle because of the "size" of this leak.

I own the car (or rather my wife does). The situation described in my original query has progressed for some time until manifesting itself in this final manner.

The center vents shut down on even the slightest acceleration but the side vents still blow cool.

The blower motor regulates the air volume coming out of the vents not the A/C compressor.

 

I had the same thing on my 94 C280. The vacuum actuator for the fresh air flap was leaking. I think you can check what line it is by pulling the glove box out. There is a solenoid bank for the myriad of Vent actuators. I remember the leaking one was green.

Bad news is that it took about two weeks of spare time to get the old part out. The best tool I had was the Haynes manual #3511. Ordered it from Amazon and it took about 6 weeks to arrive.

You can also do a fair job of tracing the vacuum leak with a hand held vacuum pump "Mighti Mite" on Harbor freight.