but only when the DEF mode is on. I just noticed it today, but didnt actually try the AC itself. Now I do know that the AC clutch/compressor is supposed to work when you use the DEF, as well as the AC. The belt was also jumping around quite a bit, more than i like. I dont have the AIR pump installed anymore. The belt tensioner was also shaking quite a bit when the defrost was on.

So is it time for a new AC clutch? Car only has about 77,000 on it, but it is still over 20 years old.

 

It's probably not the clutch making noise, but the compressor itself. Does the A/C work? If the A/C system is empty, the compressor could be running dry, without enough lubrication. It might be a good idea to unplug the compressor clutch, that way you can use the defroster without worrying about damaging the compressor.

 

No, havent tried the AC lately, but did use it some this summer, and it did sort of blow cold air. But otherwise, good suggestion on unplugging compressor clutch, so it won't cycle at all.
Now here is some more background on my situation. I changed the AC system over to the R134 in the summer of 2004. Just bought one of them cheap retrokit deals from Wallmart. I dont put many miles on my car, but I imagine it is the time passed that is the issue.
The belt I am running is about 1" shorter than stock, sicne I took the AIR PUMP out.

Next, dug out my service manual, and did some reading on the system. Looks like it could be a variety of things going wrong, maybe more than one. It could be the pressure cycling switch, since I did not see the clutch cycling in and out. Something like 6-8 times per minute is normal.

But it also could be low on refrig, which also has the oil in it. The oil lubricates the compressor. Low refrig could cause low pressure, so it wont cycle.
The compressor could also be going bad. Hard to really tell where the noise is coming from exactly, but the belt is really flexing when the clutch is engaged. And the tensioner is rocking steady also. Keep the ideas coming.

 

Quick update, checked the static pressure with my R134 gage, and it was at 45psi. So the system should be ok on refrig. I just hope that compressor is ok. Car is basically parked for winter, but the battery is still in car. I will make notes to check the system out next year for sure. Can't really do anything with it when it is 45deg out!