mystery squeal
 

I just had a new a/c compressor, drier, expansion valve, pressure switch, and belts put on my 380 SE. At start up there is no squeal and the a/c blows cold but after getting on the road and the compressor switches from on to off and back there is a bad squeal for a few seconds until it engages again. It really sounds like a belt but it hasn't done it while idling and cycling the a/c. Recently my battery has started dying and I thought the squeal came from the alternator. In fact I am certain I needed a new alternator belt and heard the squeal in the alternator area. This has been happening since way before the a/c work. Can it be that when the compressor kicks in that extra current is being drawn and the alternator is going bad? Frustrating because now it only seems to do it while moving down the road so I can't pinpoint it. Thoughts???
1985 380SE 207K

If the belts are in decent shape and properly tight they won't slip unless the loading is tremendously above design, such as with a locked compressor. Both senarios you spoke of could happen if either belt were loose. If it were the alternator then it would also squeel after starting the car with or without the AC on.

Hello El Miguel,
Check the clearance of the compressor clutch! I bet you that when it was renewed, not enough shimms were installed under the clutch plate. When the assy. warms up, the clearance becomes less and eventually the clutch doesn't release properly anymore. You then will notice that the clutch moves slowly along with the pulley. The friction noise is what you hear. Observe and add shimms as required.
All the best,
Dokta

Thanks for the replies guys. Dokta how does one go about adding shims? Does the clutch come off easily? Would my old compressor have shims that I could rob? The compressor is new not rebuilt but that sounds logical. Just today, I started the car, turned on the a/c and not a problem. Drove it to town and it started squealing within 2 miles. After shopping, I tried to turn on the a/c and it started its thing again. Drove home without a/c and parked in idle, opened the hood, hit the a/c button and it worked like a charm. If I leave it on max cooling it doesn't cycle off so.. no squeal. Perturbing.

Hi El Miguel,
Use shimms off old compressor. Most of the times you have to drop the compressor to take off the clutch. Just make sure that you can observe the friction/ noise, before you add shimms!
All the best,
Dokta