1989karr

Ok, I posted a while ago about my serpentine belt on my 1989 2.8 Bird vibrating between the new (did it with the old one too) tensioner and A/C compressor on the V-6 board. Makes some nasty noises and vibrates like a guitar string!

I was told it may be the compresor siezing up. My question is how can you tell? The air still gets nice and cold. I did nitice that when the A/C/engine is off it is nearly impossible for me to turn the compressor clutch by hand. I mean REALLY hard to turn. Signs of a bad compressor going bad?

blue86iroc

iTrader: (2)

You had the belt off when you spun the compressor pulley, right?

If the air conditioning isn't turned on, the pulley should rotate freely. It's just free-wheeling at this stage and the parts inside the compressor aren't moving. Once the refrigerant starts moving through the lines, a pressure switch is tripped that enables the compressor clutch. I'd imagine that the compressor would be harder to turn, but I've never engaged the clutch with the belt off and spun the pulley, so I don't know for sure.

You can check that fairly easily if you jump the AC pressure switch wires. On my '86, the switch was located on the drier (aluminum canister) and had two wires running to it (blue and green, I think). You should hear a *click* from the compressor when you short the circuit. Do this with the engine off, of course.

Check how the compressor spins with both the clutch engaged and disengaged, then we can see if it's related to your vibrating belt. The AC belt on my IROC was behaving so badly that I ultimately removed the whole system (I didn't use it much, anyway). That was with V-belts, but it certainly vibrated "like a guitar string." It actually started to cut a groove into my upper radiator hose!

1989karr

I just did the check and with the compressor off, and the pulley spins freely. I did it with the compressor engaged like you said and it seems seems like there is considerably more force needed to turn the whole thing. Basically you can't spin it and have it continue to spin a little on it's own. You have to turn the whole thing by your hand to get it to a certain position. Not at all like the pulley when it is not engaged. Any thoughts to it?

blue86iroc

iTrader: (2)

Sounds like it's working the way it should. The clutch is designed so that when the AC is turned off, the compressor free-wheels to reduce the load on the engine. This is why you often get better gas mileage when the air conditioning is off (less load = less power required to rotate the crankshaft = less fuel consumption).

Like I mentioned, I haven't actually spun an engaged compressor by hand before, so I can't tell you exactly how it's supposed to feel. I mainly wanted to ensure that the pressure switch wasn't leaving the compressor clutch engaged at all times, which could lead to premature failure.

With the switch shorted, see if you can wiggle the pulley fore and aft and also up and down along the axis of rotation. If the bearings are shot, there is likely to be play in the rotating assembly. Do you see any leaks around the underside of the compressor, near the shaft? The refrigerant also lubricates the bearings, so the seals may have wore down if the bearings are bad. I realize that's a lot of "maybes."

How much belt deflection are you seeing with the AC turned on? IIRC, my the belt on mine would jump up and down by at least an inch, maybe an inch-and-a-half. I was told this was normal behavior by a very accomplished mechanic, but it still seems iffy. What happens at RPMs other than idle?

You also said something about noises. When do you hear these?

1989karr

mmm...as far as the noises, they are the noises made by the belt as it flaps up and down. It never did this before. It flaps around about an inch I'd say. It only happens when the compressor is engaged. When the A/C is off it is fine.

The pulley does not move or wiggle. At RPMs other than idle aka higher RPMs the thing seems to more less even out. It only seems to vibrate at idle.

But the compressor is quite difficult to turn when it is engaged. That's the only thing I can see that is wrong with it...if that is something that is wrong

coolram62

iTrader: (2)

I had a similar problem with the 4.3 in my '95 Jimmy.It sounded like the bearings in the compressor clutch were going bad,or the compressor itself.It turned out to be the tensioner pulley.It did it's own diagnostic,oddly enough in an Autozone's parking lot,by freezing up.Went in bought a new tensioner assembly and a belt.At least once to have a car it break at a "convenient" place.

1989karr

I thought it was the tensioer actually. In fact I was positive because when I released th tension on the tensioner to change the belt, the tensioner stayed in the up position! But alas......even with a new tensioner/belt, the thing is still vibrating!

blue86iroc

iTrader: (2)

You gotta remember that the job of the AC pump is to compress the refrigerant to about 3.5 times its original pressure. The drag on a 200 hp engine is fairly noticable when you turn on the AC, so I don't think it's going to be easier to turn by hand.

Are all of the tensioner and bracket bolts tight? Can you feel any vibrations from the driver's seat?

1989karr

Yeah, I kinda forgot about that compression factor

But yes, all the brackets/bolts are tight. I don't feel anything from the seat, but I do hear the belt flapping around. I thought maybe the belt was to long but I checked again and it's the correct belt! I'm really confused here!

I mainly find third gen V-8s in junkyards, but are the compressors more less the same? Assuming I find a good one, maybe I can check to see how hard it is to turn those compressors by hand.

blue86iroc

iTrader: (2)

They should be the same, if not very similar. I can't see why GM would change anything between years besides mounting locations and pulleys. It might be worth a shot, but remember that you'll need a battery to engage the clutch on a junkyard car.