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94 Fleetwood Brougham
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Discussion Starter #1
I am getting pretty bent over a ac compressor squeal that I am fighting with. :rant2::rant2::rant2::rant2::rant2::rant2::rant2: :mad::mad::mad::mad::mad::mad::mad::mad:

I have the LT1, and factory mech fan. With it disconnected, no change. AC on, it squeals like crazy, but once it gets up to speed, it is fine and stays fine for hours on end. Shut off the engine and let it sit for a min, and back to squealing... But when I get over 50% throttle, I have AC set to shut off, and I never get a squeal when that turns it on/off.

Ok, so, what have I done? Replaced belt tensioner, replaced belt 2x (gatorback belt and el cheapo belt, second one (el cheapo) is slightly smaller) and the smaller belt helps, some. Tensioner made no difference.

So, the squeal is the compressor itself stalling. If it is on and quiet, and I am stopped, and turn the wheel, the additional load on the belt from the PS will cause it to squeal (again, stopping the compressor pulley).

The only thing left I can think of is the AC possibly overpressurized. It was perfect as per GM charts last year as well as by weight when sucked it all down and put new R134a in. But can overpressurization cause too much AC compressor loading?

Is there something else that might be causing this? What might cause the compressor to have too much load that the belt can't handle it? It doesn't feel like there is excessive compressor load, at least on the gas pedal....Unless, of course, the belt is squealing and stalling the compressor, then it is loaded pretty good.
 

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1979 Coupe Deville
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My 92 Chev P/U had this prob last year right after I had replaced the belt. Put on a new tensioner and would still squeal ocassionally. Come to find out, the dummy at AutoTwilightZone had given me the wrong belt.

Your problem, I dunno? Have you tried the "WD-40" trick? Spray the belt/pulleys and see if it stops the squeal.
 

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I am a little confused here, but overcharging the A/C is not likely your problem.
If the noise is dependent on A/C operation I'd say you could have an internal compressor problem.
Having the same problem with 2 belts indicates that you probably have the right belt.

What is this "stopping the compressor pulley"?
Maybe you could re-explain this issue so I could understand better.
 

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1992 Eldorado Touring
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94 Fleetwood Brougham
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Discussion Starter #5 (Edited)
It acts like the compressor itself is loading too heavily on the belt, the clutch is NOT slipping, you can see it very clearly, the compressor itself is nice and quiet, never makes a peep, but the belt trying to turn a compressor that is not running squeals like crazy. If you look at the compressor while it is running and the squeal is starting, you can see the compressor is trying to stop. Again, no noise from the compressor, but the belt sliding on the AC pulley makes noise that the people in the next state can hear.

So, my (warped) thoughts on AC pressures (which last I checked were low when the compressor was off, but I haven't paid attention lately) being the problem, is wondering if something in the system is making the compressor work too hard, either liquid freon (that breaks things right?) or ????? I am not leaning towards a compressor issue or a clutch issue due to no noise from them at all, the only noise is belt slippage.

Yes, there is a total of 3 belts (original, Gatorback and then now the el cheapo from Autozone, where the autozone belt is smaller than the Gatorback by around 1/4" to 3/8" as measured, the new Gatorback belt at the store matched my 5000 mile or less Gatorback belt precisely) it has done it with, when the belt is new, it is much less of an issue, but it doesn't take long to start squealing more and more.

Not running AC eliminates the issue, never a peep from no AC on. Most of the time you have to turn the AC on when the engine is running at faster (2000 rpm + rpm) and then it usually gets the compressor up to speed and then you can slow the engine rpm and most of the time it is fine and won't make any noise at all for the rest of the day, until, you shut the engine off, then you go through it all over again.....

Edit: The compressor that is in there is only around 2-2.5 years old, possibly replaced by a Cad dealer in Madison, if I can find the records, it might be in there..... And 9 months before that, the OEM compressor was replaced... Now, this compressor DOES have around 100K miles on it, but it isn't terribly old. I am no hurry to replace it, that job looks like it would suck....
 

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'80 Fleetwood Coupe, 1994 and 1995 Mercedes 140 Coupe
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Check high side pressure. A restricted orifice expansion tube and/or restriction/lack of heat exchange in the condensor will give similar symptoms. Oil overcharge could contribute to other problems that might not be troublesome otherwise.
 

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94 Fleetwood Brougham
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Discussion Starter #7
When you vacuum down the system, do you get the oil out at all (I thought it was supposed to be carried in the freon) or does it collect in the compressor (mine is lowest point in the entire system)?

I'll check the high side pressure tonight and see what it is doing. I did find the orifice plugged up last year, and it shot up to well over 500 psi as soon as the compressor kicks on (and promply blew the popoff and then shut off for a moment). Maybe more junk got hung up in the orifice again....
 

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Discussion Starter #9
Gotta dump compressor by hand?

Anyone give me a rough idea what it takes to pull an LT1 AC compressor?
 

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If the A/C pressure gets high enough to stop the compressor there is a relief valve on the system that will vent refrigerant.
I have seen pressures go as high as 450 psi without the belt slowing down.

It sounds to me like the compressor itself is going bad internally, mechanically binding or locking up causing this to happen.
Either that or the belt is just wrong.
Are you 100% sure you have the belt routed properly?
Are you 100% sure it is the right belt for the car? I think it would be odd that you got two belts the wrong size.
If the belt is just slightly too loose, when the compressor builds regular operating pressure it could slip causing this also.
It is rare that a compressor would fail internally in this fashion.
I am suspicious that there is still a belt or tensioner issue here, but I can't put my finger on the real problem.
 

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You need to check the a/c pressures and note the pressures when the squealing starts. If it is high, your electric fan should have come on. If not, that circuit is faulty. Also, the clutch fan must be observed to be working properly. If you don't have easy access to gauges you could direct a garden hose at the condenser at the time of squealing. This will drop the high side pressure and if the noise stops you must gauge the system and correct the problem. If you do try the garden hose routine, be sure to NOT allow spray into the belt area. Changing the compressor on an LT1 is not a fun job. Changing it when it may not be necessary is even worse.
WMD
 

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Discussion Starter #12
Mine would popoff around 500-550 psi (on my budget gauges, mine went nutty over pressure when the orifice plugged up), no squeal then.... But that popoff sure was loud and freak you out when it would popoff!

I got the first Gatorback belt from one store (Parts Place in Elkhorn, WI, one of the last of the old great parts stores, it is RARE they don't have something, they keep a worthy inventory of everything, even old stuff!), compared it to another at Autozone, and then bought the cheaper one from Autzone because it measured around 1/4" to 3/8" smaller. It helps, but wasn't it. I dropped $52 on a tensioner from NAPA because the general problem on ImpalaSSForum.com for this problem was linked to the tensioner, but that made no difference at all.

Yup, double checked the belt routing 2x.

I hope it isn't the compressor, that job on this car looks to be a pain in the caboose. But it seems so odd that it isn't noisy when it is running, it is just like initial starting load is high, but once going all ok. If the compressor was drawing too much hp, would you expect mpg loss? I am actually at or higher than I normally get this time of year (mid to high 19's with AC on, city/highway), which is normal with it in the 70's and 80's with AC on.

I'll try to get out and check AC pressure here before I leave for work.

Now, the puzzling thing, for about 2 seconds at first start, I am getting a squeal that I can't pin down, it happens too quick. I can't tell yet if it is the AC momentarily on at the time I start it (with AC controls off) or ?? I can't move that fast! It almost sounds like the alternator. I have another alternator front housing/rotor assy (actually the original one) that I can put on to eliminate that this weekend.

Would a dragging alternator front bearing take enough power out of the belt that the AC could stall? It doesn't seem to make sense to me either....

I just don't know....
 

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Discussion Starter #13
I'll try to do here, good idea on the garden hose. Not sure on fan, haven't paid attention, it does work as it always has. Clutch fan works perfectly.

I'll go try now if I can find my gauges.....

You need to check the a/c pressures and note the pressures when the squealing starts. If it is high, your electric fan should have come on. If not, that circuit is faulty. Also, the clutch fan must be observed to be working properly. If you don't have easy access to gauges you could direct a garden hose at the condenser at the time of squealing. This will drop the high side pressure and if the noise stops you must gauge the system and correct the problem. If you do try the garden hose routine, be sure to NOT allow spray into the belt area. Changing the compressor on an LT1 is not a fun job. Changing it when it may not be necessary is even worse.
WMD
 

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Discussion Starter #14
Well, I ran the pressures, they were actually a tad low, I toss in some freon to get them closer to the book (was 20 psi low side, 160 high side, doors open, hood open, 2000 rpm, compressor was cycling on/off). Book says @ 70F, 70% humidity around 240 psi high side, I have it closer to 200 now, still might be needing more, but for now, I will wait till I can verify humidity, today I could not, so I went to the low side of humidty on the charts.

Didn't fight me near as much as before, but still a quick stab of the gas it will squeal. I don't see the compressor stalling now like before, but then again, it generally doesn't after rain or during rain, which we got a lot of last night.
 

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Discussion Starter #15
According to my 94 Fleetwood FSM:
60% Relative Humidity (I can post more humidity's if needed, most are very close to these numbers) These pressures are @ 2000 rpm, all doors/windows open. Fan blowing through condensor if you don't have mech fan option.

Ambient Temp....Max Low Side....Max High Side.......Outlet Temp F
70....................23..................200.....................43
80....................36..................315.....................56
90....................43..................365.....................64
100..................55...................375....................78
 

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Low pressure won't cause the compressor internally to slip the belt on its pulley neither will a seizing alt. cause the belt to slip on the comp. pulley. The belt will slip only on the seizing unit. Your last posts indicate low a/c pressures but also that the squealing did not occur during the tests. Here are some thoughts. 1. You need to observe the pressures when the squealing is happening. 2. Be absolutely sure that it is the compr. internally that is stalling. It could be the clutch shoe on the pulley or it could be the clutch Pulley Bearing itself and Not the compr. internally. 3. Remove the belt and spin all pulleys by hand to check for roughness. No roughness is allowed. 4. Be sure you have the Correct belt routed Correctly and that it is properly tightened by the correct tensioner.
WMD
 

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Discussion Starter #17
Well, got it to squeal with gauges on, anytime squeal is present, pressure no longer builds and if long enough stalling, starts to lose pressure till the belt gets enough traction.... and then comes back up......

Yes, you can see the clutch stay locked and the pulley/clutch assy lose speed together. When I spun by hand, it felt ok, it didn't seem at all abnormal.
 

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Good ,You got it to squeal with the gauges on. You also found for sure that the compressor is causing the belt to slip on the compressor pulley. Am I correct? If so, what were these pressures at the point of slippage? If the high side was excessive were both your cooling fans on? and was the low side too low or normal. Of course if the electric fan did not come on or if it was lazy to start, that would be your problem. If the pressures were not excessive and the belt slipped I would be looking very closely at the belt routing. You need to have proper belt wrap on that a/c pulley. If all of the above is normal and the clutch fan is truly operating properly with the electric fan at the squeal point, then you have to look at the compressor. I have never seen a comp. seize up occasionally without showing other signs of failure such as noise or poor performance etc.
When you are diagnosing don't forget that the garden hose can be helpfull. :)
WMD
 

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If the belt is slipping, a/c pressures are within normal range, the compressor is not compressing anymore and the belt starts slipping on the pully with the clutch visibly slowing down your options are limited to about one that I can think of.
Something freaky is going on inside that compressor.
I agree, I have never seen this type of failure.
But from here, it just sounds like your compressor is dying a slow and painful death.
 

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If the compressor itself is causing enough drag to make a good belt slip then it will surely launch itself soon. Maybe the new belt tensioner is defective. Is there a chance that one of your other accessory drive pulleys have been changed to a different diameter?
 
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