Hey

I've recently replaced the AC compressor, drier, Orifice AND the condenser on my wife's jag and the AC keeps doing the same thing: When the engine heats up, the compressor clutch starts slipping. I was wondering if the engine is overheating, causing the compressor to shut down. I replaced the water pump about 2 years ago. The gauges read normal(are these even reliable?). I noticed a coolant leak when I replaced the compressor, it went away when the system was put back together. I'm about to wave the white flag here and take it to -gulp- the dealership. Before I do, I'd like your help please.

Thanks!

 

Bauldee, when you turn on the A/C system, do your cooling fans immediately turn on? If no, then you are suffering most likely from a bad fan control module.

Now, with this being said, if the freon loop is not cooled properly, it will reach excessive pressures and one of the pressure switches will shutdown the compressor until the pressure returns to normal (ie, freon is cooled). So, it is possible that not getting sufficient cooling across the radiator can lead to the system shutting down. Now, with that being said, does this same sort of thing happen if you are driving down the highway at say 60 mph? If so, then you can rule out the cooling system as the fans pull less air at max flow than is coming through the radiator due to air coming in through the grille. This would lead me to believe that you have a wiring issue with the clutch, leading to insufficient clamping force for the clutch. IF you need help troubleshooting this, let me know.

Hopefully this will get you going in a general direction. From there, we can get you further towards a solution.

 

Also, I will ADD, if you are a little overcharged in the system, this will cause Compressor seizure and lock up...It don't take much to be overcharged on these systems.

 

Thermo

The fans respond immediately. The clutch starts slipping when the engine warms up. What you said about the freeon not getting cooled makes sense. I put on of those gauges you get at autozone and when the clutch slips, the pressure goes through the roof. Now is the clutch slipping because the system gets over-pressurized or is the system getting over-pressurized because the clutch is slipping? Since I've replaced everything except the evaporator core(please don't be the issue), I'm starting to think excessive heat might be the issue? As I said, it seems to run fine when the engine is cold.... As far as going down the road at 60mph, it still seems to do it. I can test this again.
As for the electrical, during the 2nd compressor(This is my 3rd), I got some leads on the compressor wires and was reading a steady 12v even when the clutch was slipping. If there's another way to troubleshoot the electrical, I'm all ears.

Thanks for the response.

 

Colt, The autozone gauge seems to be reading in the "green". I know it doesn't mean much to an AC expert as they use diffrent gauges. However, the car has done this with 3 diffrent compressors.

 

Same Compressor Clutch?..if so, Thermo maybe on to the right track, that the Clutch is weak or worn..Going by that you said AZ proved normal pressure ranges..I teach Commerical and domestic refrigeration and Thermo-Dynamics of Refrigeration for many years, it has been my experience that there could be a multitude of possible reasons..We just got to eliminate all the obvious causes first.

 

The clutch/compressor combo is brand new. I'll give you the highlights:
1. Found original compressor dead. The clutch fuse was blown. The clutch had shattered pieces on the top part.
2. Replacement compressor goes in. No drier. Added freeon myself. Clutch started slipping. Took it to NAPA, they said: Bad compressor.
3. 2nd replacement goes in. Had it evacuated at a garage prior to compressor replacement. Had same garage leak test and fill after compressor replacement. Clutch slipped.
4. Went to an AC shop with 3rd (New)replacement compressor, drier and orifice tube. AC shop "flushed" it and recommended a new condenser. OK. The orifice tube had a few metal shavings(about 20 SMALL pieces), Tech told me that it MIGHT have been the problem. THe orifice tube was not blocked. Charged system. A month later, Clutch slipping.

Other than the evaporator core, I'm thinking the obvious causes have been eliminated. That's why I brought up the overheating questions.

Thanks for the responses guys. If anybody else has heard of this, please chime in.

 

Last question for certainty..After the last compressor change out along with all the other components..was a Complete Vacuum (evacuation) pulled on the system, prior to adding any refrigerant?

 

Bauldee, if your pressure is shooting sky high, then the compressor is still turning on the inside. If the clutch is slipping, the compressor will not compress the freon, therefore your pressures will remain low. What you are experiencing is sounding like the compressor is raising hte pressure too high and is getting overloaded, forcing the clutch to slip. The overpressure switch should cause the clutch to disengage and this will cause the freon to slowly loose pressure.

If you want some wiring help with the clutch engagement circuitry, let me know. THe overpressure switch should disengage the clutch when the system pressure rises to something in the neighborhood of 550 psi as I recall. I would need to double check the JTIS for the exact setpoints.

 

Colt: The tech who worked on it claimed they did. Fletchers said they did during "Compressor 2".

Thermo: So we're talking about the AC pressure transducer? I saw this on the JTIS. So it works as an OVER-pressure switch? I guess that makes sense now. The only thing is that I have no IDEA where it plugs into. I also would have to figure out if a signal is even being sent? YES, any help or diagrams would help me out. I will start researching the who sells the part and prices(among other things). The only bad thing is that: if you replace the transducer itself, the system must be evac'd and re-charged.

I'll wait until my wife gets home and I will hook up a meter to the pressure transducer.

Thanks