What does it mean when I hear belt squeaks that STOP when I engage the A/C? (1 Viewer)

[DocuDude]

Hi,

After lots of PM fun, I finally started my truck today after a month of working on it.

She started up beautifully, I took her around town (20 min, never going over 35mph) with full heat, as I am in the process of running water through the coolant hoses to flush.

Anyway, I noticed there is a belt squeak when I am running.
However, when I engage the A/C, the squeak goes away.
What does this mean???

Other small details that may have meaning to Cruiser detectives:
I broke my knock sensor during PHH replacement and will be fixing this wekeend, I got the P0330 code, just in case this is the reason for squeak (though I dont think so).
+
Also, there was a squeak before I started wrenching (unsure if it stopped with A/C on), and the A/C belt seemed loose to the touch, so I did tighten it while I was doing my PM (perhaps I overtightened / still not tight enough?)

 

[gbeltran]

Probably the AC clutch, it has a bearing that allows it to freewheel when not engaged, maybe that's going. I'd also take a look at the idler pulley, it too has a bearing that can go bad, but that would probably squeak even when the compressor was engaged if it was on it's way out. That ones much easier to deal with however. I'd try snugging the belt up more before any of that.

 

[western flyer]

Belt may have been "done" before you started. A slipping belt will wear down the belt "bulges" that are needed to properly grab the pulleys. The belt bulges out a bit on the sides as it bends over a pulley. Time to replace?

Edit: My point above is that a belt needs to properly grab the sides of the pulley (see pic below). if the belt in this case is worn (material removed from the belt-pulley contact surface of the "V") from slipping on a pulley then it is likely this belt would have to be over-tightened in order to keep it from slipping in the future. Over-tightening a worn belt in an attempt to keep if from slipping is no solution, in part due to bearing wear. I would start with a new belt here, at the proper tension. I hope that makes sense.

stolen from the web:
Assure Proper Belt Tension – Proper belt tension is usually not an exact science, but is important for long belt life. Too little tension causes excessive heat and noise, and can cause the belts to slip and “pop”, reducing their life. Too much tension causes band breakage, and dramatically decreases bearing life, due to excessive radial loading.

 

[gbeltran]

Belt may have been "done" before you started. A slipping belt will wear down the belt "bulges" that are needed to grab the pulleys. Time to replace?

Belts easy enough to replace, please explain the "bulges" part, never heard that before.

 

[DocuDude]

I replaced the belts 8 years ago.
They have around 50-55k on them.

 

[1972FJ55]

I would suspect a loose belt and when the A/C is engaged, it loads the belt, stopping the squeaking.

 

[Hornd]

Make sure the belt is propery tightened.
May I suggest?