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HR6 Clutch Beyond Toast - Diamonds Are Next Step

terryk on Tue October 06, 2009 4:36 PM User is offline

Year: 91
Make: Pontiac
Model: Bonneville
Engine Size: 3800
Refrigerant Type: R12
Ambient Temp: 90
Pressure Low: 70
Pressure High: 70
Country of Origin: United States

A buddy brought his 91 Bonneville over saying the AC was working fine (hot day around 90F) and then it started to blow warm, then cold, then warm, etc. cycling every 10 seconds or so. After about a minute of that he said he had major smoke blowing out from under the car. He pulled over and something was burning and sizzling down near the AC compressor. He killed the AC and came over to my place (very short distance).

The clutch is fried to the point of falling apart. Roasted. More that roasted. The charge is still there but I don't dare apply power to the clutch.

In thinking about the cause, if the cycle switch shorted, the pressure could go through the roof but the high pressure switch should have caught it. I would have expected the belt to start at least making noise but the belt looked fine.

I disconnected the belt and can spin the compressor plate (and I assume the compressor guts) but the clutch is nearly ready to fall apart.


I haven't pulled the clutch off yet but I am perplexed how the clutch/coil could burn up unless it just shorted out itself enough to light on fire but not blow the fuse.

Anyone seen an HR6 clutch/coil self-destruct like this?

TK


JACK ADAMS on Tue October 06, 2009 6:50 PM User is offline

Well I would start off by leaving the compressor un-plugged and make sure the fans are working. Next see if you still have refrigerant in the system. Quick cycling is most common with either low or high pressure, but with the clutch smoked I would run with high pressure on the Hi-side. Let us know and good luck..

Chick on Tue October 06, 2009 7:18 PM User is offlineView users profile

If you only have 70psi on the high and low side and it's 90 degrees, your system is low, and thats what caused the quick cycling.. Do as jack recommends until you can change the clutch assembly, Yes, clutch bearing do go, and once they start to go, there is no stopping them, they rub against the coil, cause a lot of heat and the clutch can come apart.. Find and fix the leak while you're at it.(the excessive heat could have blown the front seal...) . You may need nothing more than the leak fixed and a new clutch assembly.... Worse case scenario, a new compressor and system flush with accumulator O tube..

-------------------------
Chick
Email: Chick

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Freedoms just another word for nothing left to lose

terryk on Tue October 06, 2009 7:37 PM User is offline

No, no, no. That's static. As I said, the clutch is toast. Toast. Carbon. Kaput. Nearly Vaporize. There is no way I would even consider powering up the clutch. At best it would let me roast hot-dogs on it as it consumed the remaining parts. It's not really a clutch anymore. It's a mass og metal and plastics.

I checked the wiring and if I hit the switch, there is 12V at the clutch. No fuse blew. I am trying to figure why.

I am leaning towards a failure of the clutch coil itself but I figured I'd see if anyone has seen this before. In other cars, if the compressor power lead gets grounded, it blows the 25A fuse. Not this time. Of course 12V at 20A is 2400 watts and that does make a decent toaster.

If the relay stuck, I guess the pressures might not get to the high pressure limit. If the compressor froze I would think the belt would complain. He said it didn't make a sound and the belt doesn't show any thing at all. Still looks fine. The compressor will spin although it seems a tad easy. Some HR6 turn easy anyway and work fine.

And yes, the fans for the condenser work.

terryk on Tue October 06, 2009 7:39 PM User is offline

Yes, the system is still charged. How much isn't known until I evacuate it but at first glace, if it lost anything, it wasn't much. There aren't any oil leaks anywhere nor around the clutch area (what remains).

NickD on Tue October 06, 2009 11:21 PM User is offline

How is this for a scenario, corroded ignition, clutch coil relay contacts, and connector contacts all dropping a bit of voltage here or there that is intended for the clutch coil. With a weak magnetic field and load on the clutch, it gets red, seen the red hot, since the coil is buried under the idler pulley, also apart of the clutch, the coil also gets red hot burning off the insulation from the magnet wire, as turns short out, the magnetic field even gets weaker causing more clutch slippage. Yup, I seen that smoke before. If the compressor seal wasn't overheated and not leaking, can replace the entire clutch, coil idler pulley and hub. But more than likely you still have that single lip seal that is a leaker. Still using R-12? If someone dropped in some R-134a, super high pressure also can stress the clutch. Just some stuff to check out.

Yes there is a reason for failure, always a reason.

terryk on Wed October 07, 2009 1:16 AM User is offline

Quote
Originally posted by: NickD
How is this for a scenario, corroded ignition, clutch coil relay contacts, and connector contacts all dropping a bit of voltage here or there that is intended for the clutch coil. With a weak magnetic field and load on the clutch, it gets red, seen the red hot, since the coil is buried under the idler pulley, also apart of the clutch, the coil also gets red hot burning off the insulation from the magnet wire, as turns short out, the magnetic field even gets weaker causing more clutch slippage. Yup, I seen that smoke before. If the compressor seal wasn't overheated and not leaking, can replace the entire clutch, coil idler pulley and hub. But more than likely you still have that single lip seal that is a leaker. Still using R-12? If someone dropped in some R-134a, super high pressure also can stress the clutch. Just some stuff to check out.



Yes there is a reason for failure, always a reason.

I agree. The logic is there. That fine line between no slip and finally not driving the compressor.

It's still R12, no conversion. I've never seen a clutch go up like this one. I'll pop what's left of the clutch off and look at it closer. I hope the bearing is good. We will see.

Thanks for the input!

Terry

NickD on Wed October 07, 2009 7:07 AM User is offline

Dead giveaway would be the surface of the idler pulley is all burnt that cause the heat, if it melted the coil, it also melted the plastic retainer for the double roll bearing and all the balls will be black and to one side. Believe a whole new compressor including the clutch is only about 50 bucks more than just buying the clutch, best to change all of it. But see what you got first. Bearing is crimped in, so not the easiest to change, they do make a crimping tool, but after 18 years, the cast iron hardens, so it does a better job of chipping off the metal than to deform it for a new crimp. Like trying to cut old glass.

terryk on Wed October 07, 2009 3:34 PM User is offline

From you comment and reading some stuff here, I will break the news to him that a new compressor and system flush is in order.

Thanks!

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