Mark944na86

I noticed today that the alternator belt was not turning the a/c compressor, i.e. the compressor hub was not spinning even though the belt was trying to drive it.

Yikes. I was surpised there wasn't a burning rubber smell and lots of smoke. I turned the engine off, and I will verfify the compressor is seized tomorrow morning. I'm not sure how long it's been like this, although probably not long, as I wouldn't expect the alternator belt to last long like that.

My question is what are the possible failure modes here? The aircon system switch was not on, so the electromagnetic clutch should not have been engaged, which makes me think possible the bearing is shot, rather than the compressor internals are seized.

I've just got the car running today with a new clutch installed, and was testing this out when I noticed the compressor problem. The clutch blew up at a track event a few weeks ago (it's taken me all this time to the get the new clutch installed), and I'm wondering whether I might have destroyed my compressor bearing on the same day -- unrelated failures, except for the hard revs on the track (BTW, I wasn't running on the track with the aircon engaged!) I'm 99% sure the a/c was working OK on the way to the track, which was the last time it was driven.

Anyway, odd. If anyone else has had the compressor fail in this way, where is it is seized when not engaged, it would be interesting to hear what the nature of the problem was. Also, any diagnostic tips to help determine the exact nature of the compressor failure appreciated.

Luis de Prat

Did you overtighten the accessory belt?

That may have killed the bearing right there.

My brand new replacement compressor from Porsche failed after only 3 years and I'm suspecting I overtightened the alternator belt when I did the timing belt job on the S2.

Found a refurbished one for really cheap on Ebay and never looked back!

Mark944na86

Possible, I guess (although the fact that it's slipping on the seized compressor hub rather than squealing and burning suggests its not overly tight) - what tension is correct for the accessory belt? Is there a specification somewhere?

Mark944na86

Oh, and how cheap was "cheap"?

Mike C.

There is a spec in the FSM on tightening this belt but it is using the gold-plated facotory belt tension tool (same one used for cam/BS belts). I have one but never use it for this purpose. I adjust it so I can push/pull the belt between the crank and AC pulley by about 1/4 inch (in the middle). I had a compressor 'seize' when one of the reed valve bolts came loose.

Mark944na86

Figures.

Sounds about right -- I will test.

What/where are the reed valve bolts?

Luis de Prat

US$ 245 plus US$ 78 shipping to continental Europe, from Texas, U.S.A.

Not bad, considering Porsche charged me € 1,300 for a new one 3 years ago.

wi54545

I had this happen on one of my 951s. The compressor clutch seized, snapped the belt. I sourced a cheapo compressor, robbed the clutch from it, and it worked great. 20 bucks and some rental tools from Autozone.

944Ross

I like to tighten by ear -- set it on the loose side, start the car with lights on, listen for squeal. Tighten until there is minimal squeal (not necessarily "no" squeal). It ends up looser that way, than if I did it to a specific tension. No problems so far, on any of my cars.

Mike C.

Reed valves are in the guts of the compressor. They are basically springy flat steel rectangular 'flaps' that are bolted one one end to a plate in the compressor in which there are holes (under each flap). They act as one way valves for compressed freon.