Slipping A/C clutch

[Mike Holleman]

I'm on my second clutch on the Classic Air system I put in my Tempest. The original one worked great for a season and then started squealing on start up and later all the time. I replaced the clutch several months back and it was fine but now it is starting to slip again. What could be causing this? It is properly shimmed and there doesn't seem to be a voltage drop.
Any A/C pros out there?
Mike Holleman

[ProTouring442]

Honestly, it really sounds like a voltage problem. With the clutch engaged, check for voltage between the negative terminal on the compressor, and the negative terminal of the battery. I'm betting on a bad ground.

Shiny Side Up!
Bill

[Mike Holleman]

I'll check that. Someone had told me that the system being overcharged could cause excess strain on the clutch. Any truth to that? I really need to get this corrected before heading to Pigeon Forge.
Gonna need my A/C.
Thanks
Mike Holleman

[ProTouring442]

I'll check that. Someone had told me that the system being overcharged could cause excess strain on the clutch. Any truth to that? I really need to get this corrected before heading to Pigeon Forge.
Gonna need my A/C.
Thanks
Mike Holleman

Not really... if it were too overcharged, the blow off valve would let go.

Shiny Side Up!
Bill

[HILROD]

It can be overcharged enough to cause the clutch to burn up. That is a common problem. If a little freon is good, more is better.

[formula]

Replace it with a 12" mcleod.

Hey, it'd be unique.

[vintageracer]

If you are running a 134A system, the high side pressure can be critical. Overcharging will cause excessive high side pressure. This causes problems for the compressor and makes it harder for the compressor to turn.

I would definetely check my pressures with a gauge. Remember, it takes a lot less 134 to fill a system than R12. Since you have an aftermarket system, make sure it is filled properly per their recommendations.

Second, the clutch setup as mentioned above is also critical and you state this dimension is correct. You did not state the type of compressor however I would guess it is a Sanden. These compressors and clutch give VERY little trouble. Since a clutch costs damn near as much as a complete compressor/clutch combo, I would give serious consideration to replacing both this time. If you are running a GM A6 compressor that is a rebuilder from the Zone or somewhere like that, this is likely your problem. I have had very little luck with rebuilt A6 compressors from anyone. Particularly since most rebuilders do not replace that little ceramic seal that is hard to install and that seal is somewhat expensive. If you have an A6 compressor, spend the money and update to a Sanden compressor. You will be glad you did!

You should not be having this problem IF you have a Sanden compressor. Call Classic Air and bitch a little bit since they loaded you up with their system!

[Mike Holleman]

It is 134A and a Sanden SD7. I installed it about three years ago. The clutch trouble began about a year ago. And the trouble started a few months after a recharge. It could well be overcharged. I'll have it checked as I don't do freon. Classic makes a nice system but they lost me when I needed the clutch and they only sold it with a compressor. Hot Rod Air had what I needed for about $80.00. I have since installed several of Hot Rods units with good results. Thanks for all the help.
Mike Holleman

[ProTouring442]

If you are running a 134A system, the high side pressure can be critical. Overcharging will cause excessive high side pressure. This causes problems for the compressor and makes it harder for the compressor to turn.

While I'll agree that overcharging can cause excessive high pressures, my experience has been that overcharging with 134A usually causes pressures so high that the high pressure relief valve lets go the first time the car is driven in any real heat.

That being said, as the problem came about just after the system was recharged, I would have a look at it. Definitely check that ground as well though, as it still sounds like a ground problem to me.

Please let us know which it was, and if it was overcharged, what sort of high side pressures you were running, I am very curious!

Shiny Side Up!
Bill

[72Z/28]

I have the same problem as well. I bought the car, and it came with the serpentine system, March Pulleys, and Sanden Compressor. The clutch was squealing or spining when reving the engine at high RPMs in neutral.

It does not make that noise anymore. Also, i noticed that it is out of 134A. It migh have been overchaged with 134A when it was squealing, not sure though..

[Mike Holleman]

I ran a seperate ground direct from the battery with no change.
Hopefully I can get someone to put gauges on it this week.
Mike Holleman

[ProTouring442]

I ran a seperate ground direct from the battery with no change.
Hopefully I can get someone to put gauges on it this week.
Mike Holleman

Bummer.... Too mad you aren't closer, I'd invite you over and we could throw a set of gauges on it.

And you're sure it's the clutch that's slipping, and not the belt, yes? As the clutch is a metal to metal contact, they usually burn up when slipping.

Shiny Side Up!
Bill

[Mike Holleman]

Thanks for the offer. Definately the clutch slipping. It's a March serp. system. It squeals as you try to bring up the Rpm's. It would burn up if I didn't shut down the A/C. I'm having a local shop check it today.
Mike

[ProTouring442]

Thanks for the offer. Definately the clutch slipping. It's a March serp. system. It squeals as you try to bring up the Rpm's. It would burn up if I didn't shut down the A/C. I'm having a local shop check it today.
Mike

Cool, let us know what they find. I am very curious!

Shiny Side Up!
Bill

[Mike Holleman]

It will be Thursday before they can service my A/C. I'm having the system evacuated and refilled with 24 oz. 134A as per Classic's specs.
The previous charging was done by a buddy at a local performance shop. I doubt he weighed the load. If the clutch still slips, I will have to guess that the damage is already done and just replace it. I did add a ground from the block to the compressor just to be sure.
Mike

[ProTouring442]

It will be Thursday before they can service my A/C. I'm having the system evacuated and refilled with 24 oz. 134A as per Classic's specs.
The previous charging was done by a buddy at a local performance shop. I doubt he weighed the load. If the clutch still slips, I will have to guess that the damage is already done and just replace it. I did add a ground from the block to the compressor just to be sure.
Mike

I know this is frustraiting, but at least you have your head on, and are looking into things one at a time. You may also want to chec the voltage at the compressor if it's still slipping. Maybe the clutch isn't getting enough juice? I know in my original answer, I kind of took that for granted, something I know I shouldn't do! Just ask me about the time I cleaned and rebuilt the carbs on my Triumph Bonneville four or five times, sure it was running lean. It wasn't, it was an electrical issue.

Shiny Side Up!
Bill

[Mike Holleman]

We have all been there Bill. The voltage was the first thing I checked. Here again no change with a direct from battery 12 volt feed. I spoke with Hot Rod Air this morning and they suggested that the belt might be too tight? It's not.
Mike

[KUL FIR CHICK N]

You're most likely overcharged. If you don't have a pressure safety switch in your system, you definitely need one. All systems should have one. There is no pressure relief valve in that system, so if you don't have a switch, you are likely to ruin your compressor, and possibly injure someone when a hose blows.

Also, check your fan. If its a clutch fan, make sure the clutch is good. If its an electric fan, it should be triggered by a "trinary" switch, which is a combination safety switch/fan signal switch. It is located in the high pressure line. There must ALWAYS be good air flow through the condenser when the system is on. Without the fan on, you can reach 400psi in about 15 seconds on a hot day.

Many shops claim to know what they're doing on an A/C system, but we often find that the "expert" A/C guy at the local shop is the one most likely to mess up your system, because he thinks he knows more than he does and therefore ignores the manufacturer's recommendations. Some shops also add oil when they shouldn't. Too much oil will have the same effect as overcharge.

Bottom line, you really can't do a good job of troubleshooting the system without a set of gauges on it.

It sounds like neither of your suppliers did a very good job of helping you troubleshoot your system.

[ProTouring442]

There is no pressure relief valve in that system, so if you don't have a switch, you are likely to ruin your compressor, and possibly injure someone when a hose blows.

Ah... I assumed it had a relief valve. Well, you know what they say about assuming, eh?

Mr Chick Fil-a here is correct though, if there is no relief valve, pressures can get out of hand very quickly. Especially with 134A. When we charged my father's car, there aboslutely no specs to go by (Firebird evaporator, Corvette compressor, Buick condenser, plus whatever lines). While charging to see, we watched outlet tempsas well as high and low pressures. It only took a very small overcharge to cause high pressure to zing past 350psi. It's my understanding that, on a 134A system, there should be gas pockets in the post condenser liquid line. With R12, this isn't so (hence the old sight glass systems).

Shiny Side Up!
Bill

[Mike Holleman]

OK, There is a binary safety switch on the dryer. The twin 12" fans are switched on with the compressor. I didn't use a trinary because the fans are switched on the negative side by way of a relay as per Spals instructions. Just in case the clutch is already toast, Hot Rod Air has a new one on it's way to me.
Mike