Serpentine Belt Jumping Around

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cchase

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The A/C in my truck has been dead for a few years. The other day I came across a few cans of R-12 and decided to recharge it.

After filling it up, I noticed that the serpentine belt was jumping around on the input side of the compressor. At one point it jumped around enough to come off the idler pulley entirely.

The alignment of everything is correct - the belt only jumps around when the compressor is running, but the compressor is operating correctly. It's as though the belt is stretching enough that it flaps and that causes it to wander on the idler pulley.

What is causing this? Old belt?
 
+1, I was getting funny squeaks and jitters out of the blue on a Goodyear gatorback belt I was otherwise happy with. Putting a new gates fixed that...
 
Is the system overcharged? If the compressor pulley is hard to turn due to overcharging, the belt can jump around and slip on the pulley. Did you draw down the system with a vacuum pump before charging?
 
Also it could be that the tensioner is shot. The spring, pivot, and bearings for tensioner puley all wear out. If you have over 50 K on the tensioner it is probably a good idea to replace the tensioner when you replace the belt.
 
Inspect the belt for excessive cracking or damage and that is the correct length. As long as the belt is the correct length and in good shape, I think its more like the tensioner is gone. If it is not putting enough tension on the belt, it will move like that. The tensioner should only move about .5" or so between A/C on and A/C off. The belt does stretch or get wrapped up around pulleys when it is put under load. If its letting the belt jump like that, its cooked.
 
Old serp belt & tensioner would be my first guess. I would investigate them more (or just outright replace them) before looking into the compressor.
 
Try revving the engine with the AC off.
As you go up and down, there should be some movement in the tensioner. At steady state speed, there should be very little.
this would show the blet is not loose/tight/uneven, and that the tensioner is not horrible.
Your AC may be dragging heavily or otherwise faulty. This is #1
Of course a tensioner maybe a problem, but so [censored] it points to the AC.
Some movement is normal, as the AC cycles.
 
Thanks for the replies.

The current belt is a few years old and I have a new one sitting around so that will be the first step.

As far as the system being overcharged, it has a leak and hasn't been used in 3 years because it got low enough that the compressor wouldn't kick on. Total system capacity is 40 oz. and I put in about 28-30 oz.

Nothing sounds or feels wrong with the compressor.

The tensioner is original so this could certainly be a problem but it operates properly as long as the compressor isn't running, I've never had slipping or alignment problems with it and the tension feels good to me when I had to put the belt back on yesterday. Again if the new belt doesn't fix it, I'll have to take a look at it closer.
 
Originally Posted By: cchase
As far as the system being overcharged, it has a leak and hasn't been used in 3 years because it got low enough that the compressor wouldn't kick on. Total system capacity is 40 oz. and I put in about 28-30 oz.

Nothing sounds or feels wrong with the compressor.


28-30 oz. of refrigerant doesn't mean it's not overcharged. The new belt might just be masking the problem. If there's a leak in the system, it let out the pressure and let in atmospheric gases. That will reduce the efficiency somewhat and could lead to overcharging. If you used refrigerant that has oil in it but the system wasn't leaking oil, it could also be over-oiled. Since the oil isn't compressible, this can behave like an overcharge condition. I would check the high and low pressures after the system has been running on recirculate for a few minutes. Not sure what the spec should be for your car, though. Maybe an A/C expert will chime in here and tell me I'm crazy. Wouldn't be the first time.

Of course the ultimate solution would be to fix the leak and then draw down the system and recharge, but I've milked them for a few years by recharging as needed. When I overcharged, the belt jumped around as you described.
 
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You bring up some good points. I don't know much about the technical details of vehicle A/C units.

I will say that the compressors inability to turn on, to my understanding, would indicate that there is no pressure differential between the high and low side and probably means there was little to no refrigerant left in the system.

When I compare where the tensioner was with the old belt to the new belt, I'm pretty easily convinced that the tensioner was already bottomed out and simply couldn't tension the belt further when the additional drag of the running compressor was added.
 
there is never any pressure difference after only a minute or two of sitting no matter the state of charge.

Pressure rapidly equalizes as the system is shut off.
 
I was going to ask if you added oil when you added the R-12. I learned the hard way that you have to add oil when you add that much freon. I had a truck that the a/c had leaked down on and I filled it up but didn't add any oil. The compressor blew up in less than two weeks.
 
Originally Posted By: cchase
Replaced the belt, all is good now. Old belt was pretty stretched out.
Excellent. Thanks for the resolution.
 
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