GM 4108 - OTR A/C Compressor Squeal

[richard5933]

As many will remember, I had the OTR a/c compressor replaced last year on our 4108. The old one couldn't be rebuilt and we installed one of these:

https://truckerac.com/gm-compressor-model-a6-type-c61138002.html

The system has worked great since. It still makes very cold air, but now has developed a problem. It will squeal when running. The squeal is not constant though. For instance, I started the engine with the a/c running, let it go to fast idle, and then the compressor started to squeal. It did so for a few minutes, then the squealing stopped, then it kind of came and went for a while.

All the while it squeals, the a/c makes cold air. The belt appears to be in good condition with no visible glazing. There is about 1/2" of deflection when I push on the belt - not sure if it should be tighter. I'm afraid to over tighten and damage the bearings.

I've read a little online about this, and have everything from "the bearing is about to give out" to "not enough refrigerant" to "too much refrigerant". Also in the mix was a lot about the belt slipping, but if it was slipping that much I'd expect to see it glazed by now.

The clutch engages fully, and on the GM the clutch stays engaged the entire time the engine runs. I guess the internals of the clutch could be bad, but I am not knowledgeable about that.

So? Too much/too little refrigerant? Belt? Clutch failing? Bearing?

Anyone have a thought on this one?

[richard5933]

Bit of an update...

I double checked the belt. It's not glazed, but the rib on one edge is pretty chewed up, and on the other edge is starting down that path.

I'm guessing that the belt will be the first thing to eliminate by replacing it.

Any one know how much deflection is acceptable? I want to get it tight, but not so much so that I damage the bearings. The manual only mentions using a gauge to check, but of course I don't have such a thing.

Also, I can't see an obvious place to use a beaker bar or even a pry bar to apply pressure against the compressor to tighten it. Certainly don't want to damage it by pressing on the wrong part of the compressor.

Suggestions?

[chessie4905]

Make sure the clutch plate isn't slipping causing the squeeling. Tighten the belt some more to see if the squealing stops. If it does, you can install a new belt or leave it tighter. If it doesn't stop the squeal, try a new belt.

[richard5933]

Make sure the clutch plate isn't slipping causing the squeeling. Tighten the belt some more to see if the squealing stops. If it does, you can install a new belt or leave it tighter. If it doesn't stop the squeal, try a new belt.

How does one check the clutch plate for slipping? Is there a way to test that?

[chessie4905]

Is there scoring on the plates? Usually you can only see the surface of the inner one or rear, which is attached to innards. I've observed the slippage on them by watching the plates directly. If it is an internal problem a hookup of gauges would show excess high side pressure. Did it get a new belt when you had it repaired?

[richard5933]

...Did it get a new belt when you had it repaired?

Surprisingly, no. They put the same belt on. As I think about all this, it seems to me that I've heard this noise for a while now - on more than one occasion I'm told that I've complained about cars passing us with noise from slipping belts. (Yes, I can get grumpy when I drive - inherited this from my father.) Guess all along the noise has been coming from my engine and being bounced off the passing cars on my left.

Belt will be my first step. I just looked at the belt again and it doesn't look like the two pulleys are in line with each other, which is certainly not helping the situation.

[luvrbus]

Richard belt gauges are free most the time at NAPA or O'Rileys  ,could be the wrong belts and going to deep into the pulleys btw V belt noise can be very frustrating to find the cause V pulleys wear over time   

[richard5933]

This morning I stopped by the shop that did the compressor swap last summer to talk about this. They are going to try to align the pulleys and will swap out the belt. Sounds like at least some of the work will be done under warranty.

Sounds like a good starting point for a plan. I'll report back once I know what they say.

[bigred]

Richard Also make sure your Ac belt is running true .On my Preavy ,It has enough enough adjustment on the compressor mounting bolts to get the belt seriously out of line.

[richard5933]

Ended up being nothing but a mis-aligned a/c compressor pulley. Glad I brought it back to the shop, since they had to use a bit of force to get the mount into the right position. Now I'm wonder if this mis-alignment is what took out the OEM pump, since it ended up with a slight bend in the main shaft. Regardless, it appears to be working now without any noise.

[richard5933]

Had a great laugh when I got home and read through the tech's notes on the invoice. Usually they just detail the work they did, but this guy felt it necessary to make a very lengthy entry.

Here's the part that I found comical...

Had to figure out how to start bus. Had to figure out where battery switch was. Drove around shop, had to figure out how to get into reverse...

I did talk to the service desk about this to be sure they didn't have a total beginner working on the bus. They assured me that the guy does great work on a/c systems but was not familiar with the bus. When I took it in yesterday, I chatted for a few minutes with Felipe, who worked on the bus last time. I wanted to be sure he remembered all these things (how to start, reverse, etc). He was scheduled to work on the a/c compressor today.

Apparently the night shift saw the open ticket and thought they'd help first shift since they had an open bay. Guess I appreciate the speedy service, and I'm lucky that in this case it all worked out. For sure I'll talk to the service desk more specifically next time to be sure that no one drives the bus who is not familiar with it, at least enough to safely start and get it in gear.

[windtrader]

Sadly, another sobering instance showing the working knowledge of two stroke OTR buses is rapidly heading toward extinction. Kindof curious about what percentage of "active" bus owners are like we DIY folk or primary depend on shops for service and support.

[richard5933]

Sadly, another sobering instance showing the working knowledge of two stroke OTR buses is rapidly heading toward extinction. Kindof curious about what percentage of "active" bus owners are like we DIY folk or primary depend on shops for service and support.

What's strange in this situation is that he was knowledgeable about the 2-stroke. It was the bus itself that threw him for a loop. Gotta admit though, there are some quirks involved in starting and shifting an old GM as compared to even a truck from the same time period.

DIY vs. Shop? Can't speak for anyone else, but we do all we can ourselves. That's not as much on the engine and chassis as I'd like, but I've learned my limits over the years. Fortunately I have the option of doing either right now, depending on the specific job and how confident I feel in getting a good result.

[DoubleEagle]

This reminds me of the time (twenty years ago) when I took my Model 05 Eagle to a shop for an alignment check. The mechanic assured me that he could get the bus in the bay alright without my assistance. There was a long delay in seeing the bus move, so I went over to see what was going on. The mechanic had used the generator panel to start the engine (of the generator) and was wondering why he could not get the bus to move.