Automotive Air Conditioning Information Forum

People,

1987 Sunbird, when I switch on the ac button to activate compressor there is immediately a loud screeching sound from the comp area. It stops after about 7-8 seconds. Vents put out ice cold ac. Then, every about 5 minutes the sound comes back, then again, goes away. Could it be the loose ac belt needing tightening? Maybe low on compressor oil?

Thanks, people.

Noquacks wrote: Fri Oct 02, 2026 5:10 am Could it be the loose ac belt needing tightening?

That should be easy enough to check.

I might pull the belt, and check any tensioners and AC clutch pulley bearings for drag or noise. And maybe install a brand new belt.

Cusser wrote: Fri Oct 02, 2026 5:51 am

Noquacks wrote: Fri Oct 02, 2026 5:10 am Could it be the loose ac belt needing tightening?

That should be easy enough to check.

I might pull the belt, and check any tensioners and AC clutch pulley bearings for drag or noise. And maybe install a brand new belt.

Thanks, Cusser. Good tips. Will try those checks this weekend!

I tightened the belt a bit, actually, to the max setting, which I thought was not a good situation for a belt to tight on the max slider notch. Started the car, and the squeal almost disappeared. But i watched the belt as it turned with ac on, and the upper edge of it was wobbling a distance of say, 1/2" up/down. is that normal? It would indicate the belt could be stretched, right? Especially even with it being tightened to the max arc setting.

Noquacks wrote: Fri Oct 02, 2026 5:10 am 1987 Sunbird, when I switch on the ac button to activate compressor there is immediately a loud screeching sound from the comp area. It stops after about 7-8 seconds. Vents put out ice cold ac. Then, every about 5 minutes the sound comes back, then again, goes away. Could it be the loose ac belt needing tightening? Maybe low on compressor oil?

Your car is well within the R-12 era. As far as you know, has the system been converted to R-134a, or is it still R-12? The reason I ask is because the conversion, if completed, might not have been done correctly, causing problems now with the compressor.

It has been on R134a for 20 years. That is not the problem. But good point!

Noquacks wrote: Mon Oct 05, 2026 2:44 pm It has been on R134a for 20 years. That is not the problem. But good point!

I don't know your car's service history (not much, anyway). But if the compressor is the original since the system's conversion to R-134a, and even before that (it could be a GM R4, which isn't known to be the greatest compressor in the world), it might be starting to disintegrate internally and seize-up at times, causing the occasional belt squeal.

One way to find out is to recover the refrigerant and pull-out the orifice tube (OT). If the OT is full of black gunk and "glitter," then you'll know for sure that the compressor is on its way out.