Sometimes my air conditioner makes noise, sometimes not

[Schneiderman]

Just asking to see if anyone thinks my AC is OK. It's a 1970 duster with a 225, has 52,000 miles. I have a lot of service records with the car and I don't see anything about the AC in there, it's most likely all original. The AC does still work, but sometimes when I turn it on it works perfectly with no noise, while other times when I turn it on I will hear whining and squeaking coming from the engine compartment. What might this be, is it OK and if not what do I need to do to fix it?

 

[cudadriver]

First thing I would check is the belt tension and condition of the belt.

 

[BadAss71]

Kinda sounds to me like the compressor clutch is about to let go. Sometimes the clutch is slipping and not other times maybe?

 

[slantsixdan]

The slant-6 A/C belt setup is very prone to loosening and making noise. You need to adjust the belt tension. This is done by loosening the two 1/2" bolts that hold the idler pulley (closest to the battery), then using a 1/2" breaker bar with long handle; put the drive end of the breaker bar in the 1/2" square hole in the idler pulley bracket and lean HARD on it, pushing it over towards the passenger side of the car. If you run out of room on the idler pulley bracket's long curved adjustment slot (where the bottom 1/2" bolt attaches) then you need a shorter belt. While holding tension on the breaker bar handle, tighten the two idler pulley bracket bolts, then remove the breaker bar from the hole in the bracket.