Hi, new to the forum, but not new to auto forums. I have 4 old Mercedes so I spend a lot of time on the Mercedes forums. Haven't driven my GMC van much lately, but we have had it since new! It has 198,000 miles on it and I am planning on driving it from OK to OR at the end of the month. It is the 4.3L, with PS, AC, and the AIR pump - and is a "part of the family"!

I just fixed the AC - reman R4 compressor, new drier, condenser and converted to 134a. Works great! But, following the conversion I noticed a chirping noise coming from the front of the motor in the belt area. I assumed it was the belt and tensioner, which I replaced. Chirp seem to go way for a day or so, but now it is back. Tone of chirp changes with RPM's - and stays constant with AC on or off, so I don't think it is related to the new compressor. I have tried the stethoscope and the rubber hose technique and I just can NOT isolate the location. I have noticed tonight that it goes away after the van gets good and warm. I am probably going to replace the idler pulley, but it sounds like it is coming from the alternator, maybe the water pump??? It is a very definite "chirp", not really a squeal...

Any thoughts?? Thanks.

Ryan