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How to Repair A/C Compressor Clutch

Discussion in '308/328' started by Brian A, Sep 14, 2020.

  1. Brian A

    Brian A Formula 3

    Dec 21, 2012
    2,226
    SanFrancisco BayArea
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    1983 US 308 GTS QV
    Can the air conditioner compressor clutch on a 308 be repaired? How?

    I used the a/c extensively on a trip a few weeks ago and the a/c failed after about 300 miles. Inspection shows that the v-belt completely melted and stuck itself on the crankshaft and idler pulleys. After removing the melted belt, I confirmed that the idler wheel turns freely. The compressor pulley made a soft scraping sound when rotated by hand.

    I replaced the belt, confirmed good belt tension and started the car. With the air conditioning off, everything stayed normal. When I turn the a/c on, the a/c clutch and compressor made a metal-on-metal noise. It sounded to me like the clutch plates were slipping. The a/c system appeared to be blowing cold air so it appeared that the compressor was circulating refrigerant per normal vehicle operation.

    When I shut off the car and felt the a/c clutch after 2 or 3 minutes of operation, the clutch had become too hot to touch. I let things cool and confirmed the clutch stays cool with a/c off and gets very hot when the a/c is on. It does not appear that the belt is slipping.

    Any help or advice is welcome. Yes, I searched the threads but most of them are a decade old with not much in the way of repair help so I am hoping others have found solutions since then.
     
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  3. conan

    conan Formula Junior

    Nov 13, 2011
    336
    Is it a Sanden compressor?
     
  4. Brian A

    Brian A Formula 3

    Dec 21, 2012
    2,226
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    1983 US 308 GTS QV
    It is a York which I bought about 6 years ago.
     
  5. conan

    conan Formula Junior

    Nov 13, 2011
    336
    I guess the obvious things would be to check the mating plates for grease, oil etc and the gap between them. On the Sanden sd507 the gap should be about 0.4mm. Adjusted by shims on the shaft.

    Maybe the fuse, relay or wiring does not hold the required power to the clutch. Measure voltage at the clutch to see the drop in the wiring.
     
  6. INRange

    INRange F1 Rookie
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    Jan 27, 2014
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    #5 INRange, Sep 15, 2020
    Last edited: Sep 15, 2020
    An overcharged or damaged compressor takes more effort to turn. As a result, it will get hot and cause the belt to slip. In a short amount of time the belt will melt usually accompanied by it squealing to death. What doesn't make sense is the part where the air conditioner is blowing cold while this is going on. If the belt is slipping....the compressor is not turning.....ie....no AC.

    As to what it is.....the first step is a few diagnostics.

    1) Put a new belt back onto the compressor (you noted that you have already done this)
    2) Put a set of AC gauges on the system
    3) Start it up with the AC off (note readings on high and low side gauges)
    4) Turn on the AC and see if the compressor spins....if it does, note the readings of the high and low side gauges)

    Post the results and I am sure we can sort out what the problem is.

    The compressor clutch uses a magnetic field to engage the clutch. It is a very small distance between the plates and the sound that you hear is usually okay. If the clutch is slipping.....usually the compressor itself is at fault because it is requiring too much effort to turn.
     
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  8. Brian Harper

    Brian Harper F1 Rookie
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    Feb 17, 2006
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    Hi A,

    As INRange is implying above, I don't think the clutch can burn up the belt. The failure mode of the clutch is to spin, putting less stress on the belt. The idler pulley doesn't have enough belt wrap to stop the belt, I think it would show trauma on that pulley if it stopped. I think it points to a compressor issue. Too much oil causing hydro-lock in the compressor maybe?

    (BrianA already knows I am not an air conditioning expert)

    H
     
  9. Brian A

    Brian A Formula 3

    Dec 21, 2012
    2,226
    SanFrancisco BayArea
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    1983 US 308 GTS QV
    Thanks for the suggestion to put the gauges on the system to confirm the compressor is working. I will do that later today.

    I still suspect the clutch though. The clutch just gets too hot too fast for the heat to be coming from simple belt friction. Within about 2 minutes the entire clutch housing is scalding hot. The noise doesn't sound right either.

    It is good to read that the clutch is user serviceable. That is the first time anyone has ever said (claimed!) that.
     
  10. kcabpilot

    kcabpilot Formula Junior

    Apr 17, 2014
    994
    California SF area
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    Paul
    You can engage the clutch by putting 12 vdc to the wire at which point you can turn the compressor by hand to feel if it is binding. It's a magnetic clutch so it seems doubtful it would "slip" More likely it is contacting something or something on the compressor side is scraping and creating the heat.
     
  11. Brian A

    Brian A Formula 3

    Dec 21, 2012
    2,226
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    1983 US 308 GTS QV
    So I did a bit more diagnosis per the suggestions so far.

    I touched a 12v to the white wire on the clutch and heard it click each time I touched. I did not hear anything unusual. Unfortunately, I have already put a new belt on the pulleys so couldn't test to see how the pulley spins with the 12v engaged. I reconnected the white wire.

    I hooked my gauges to the suction and discharge sides of the compressor. I ran the engine with the a/c off and a/c on. Below are photos of the pressure gauges. Do these pressures look okay? Additionally, it took several minutes after shutting off the engine before the pressures on the two sides of the compressor equalized again.

    I confirmed that the clutch stays cool when disengaged and confirmed it is very hot when engaged. I have run out of unburnt fingers to test further.

    Any obvious diagnosis?
    Any suggestions for next steps?
    Is there a link to instructions on how to rebuild an a/c clutch?
    If I need a new clutch any suggestions as to where to get one?

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  13. INRange

    INRange F1 Rookie
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    Excellent photos.

    So both photos show the system is working. It looks like the Low side is a bit low but the question is whether this is due to an overcharge or not. The suction (low side) will show low if under charged or overcharged. An overcharged condition makes the compressor work a lot harder and will cause it to overheat.

    How did you charge this system? The only way that works is by freon weight. Has the system been converted to R-134 or is it still R-12?

    Most AC clutches can be replaced...it just takes special but readily available tools.
     
  14. Brian A

    Brian A Formula 3

    Dec 21, 2012
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    1983 US 308 GTS QV
    The system is charged with 2.25 lbs of R12 (before de minimis recharge loss). Spec for the car is 2.2 lbs. The car has always run R12. I worry a little bit that I have no idea how much oil is circulating around although it is probably in range. Does too much oil only cause a catastrophic hydrolock or can it cause milder symptoms?

    I have read that R12 systems are more tolerant of under/over charge situations than other refrigerants. If anything I would be a little low.

    I don't think it is my compressor that is overheating; just the clutch.

    Frankly, I currently can't bear the thought of recovering the R12, draining the coolant and pulling out the compressor. It is so much work. I just changed the timing belts in February 2020. I don't like it when things don't work on my car but in the interim I am just going to unplug the clutch lead again so that the compressor cannot engage. I still badly want to get this fixed though.
     
  15. conan

    conan Formula Junior

    Nov 13, 2011
    336
    Try measuring the resistance of the clutch electromagnet. I do not know what it should be, but maybe the current is too high causing it to get very hot.
     
  16. kcabpilot

    kcabpilot Formula Junior

    Apr 17, 2014
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    I believe you're overthinking it Brian. You need to concentrate on the "scraping" noise you mentioned. Figure out what's causing that and you will have located your problem.
     
  17. INRange

    INRange F1 Rookie
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    The scraping noise is probably a warped clutch plate. Clutches and compressors get warm not dangerously hot where they melt belts.
     
  18. Brian A

    Brian A Formula 3

    Dec 21, 2012
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    Overthinking it? Moi? No surprises there.

    Per the suggestion that it might be electrical, I hooked up a 12v to engage the clutch with the engine off to see if it had turned itself into a hot plate. It stayed cool.

    I think I have tested and tried every possibility now. All evidence leads to a sick clutch. If the stupid thing wasn't so difficult to remove from the car, I would have pulled it as a first step and tested it on the bench.

    Now that I know what the problem is and now that cooler weather is hopefully maybe approaching hopefully maybe I won't need the a/c for a few months. I unplugged the white wire from the clutch, replaced the wheel liner and wheel and lowered the car back to the ground.

    I may try to find an inexpensive (ha!) replacement clutch for the car for installation in spring.
     
  19. kiwiokie

    kiwiokie Formula Junior

    Aug 19, 2013
    932
    Tulsa, OK
    Standard York right? I think rifledriver posted a link to a cheap York replacement a few months back? Might be easier to rip and replace?


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  20. Brian A

    Brian A Formula 3

    Dec 21, 2012
    2,226
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    1983 US 308 GTS QV
    My York compressor is fairly new (6-ish years). It did not come with a new clutch and I had to remount my old clutch.

    I have read that the clutch/pulley combo is specific to the 3x8 car, but I can't help but think there must be more generic clutch/pulleys out there.

    If you can post the link as to where to buy new clutch for the 3x8, it would be very much appreciated.
     
  21. waymar

    waymar Formula 3

    Sep 2, 2008
    1,006
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    Wayne
    Thinking the clutch coil is standard. That is the bones of the clutch. If that is working the mechanical part should be easy to figure out what is sticking. Can’t remember if the bearing was easily accessible on the mechanical side.

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  22. Saabguy

    Saabguy Formula 3
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    Mar 28, 2012
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    Shreveport, LA
    The thing about the F car A/C clutch is that it runs BACKWARDS of most others, that is the reason (Or so I was told) that it is better to transfer your F car clutch to a new compressor.
     
  23. conan

    conan Formula Junior

    Nov 13, 2011
    336
    Maybe there is a too large voltage drop in the fuse/wiring/relay. The coil might not create enough power in the magnetic field.
     
  24. kcabpilot

    kcabpilot Formula Junior

    Apr 17, 2014
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    I think the "oddity" is that the 308 uses a quarter inch V-belt whereas most of the compressors and pulleys you're going to find use a wide multi ribbed belt. I'm still not convinced the clutch is actually the problem. It engages, the compressor is working but something is scraping on something and creating a boatload of heat.
     
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