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Thread: AC Clutch Don't Engage With 12V Jumped To Pigtail

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    Stupid Newbie DaraSue's Avatar
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    AC Clutch Don't Engage With 12V Jumped To Pigtail

    I'm having the same issue. #10 fuse is fine. Last fall I accidentally yanked the wire that goes to the compressor loose while trying to take the intake manifold off. It came apart at this junction and I can feel it click into place (I think) when I try to put it back together, but the center of the compressor still doesn't turn.

    20180506_092621_1.jpg

    It's this compressor (r-134), looks kind of the aftermarket one DMCH sells but I don't think it actually is.

    20180506_115024.jpg

    What are the odds that something else just happened to go wrong after I messed with that wire? The A/C was working fine last fall. I haven't used it all that much (probably less than 8 hours total in almost 2 years, mostly for less than 20 minutes at a time if I'm in stop and go traffic, once for a few hours on the way back from Vegas). The compressor was replaced by the seller and the lines were replaced at DMCMW after I bought it (it still had the old R12 fittings). They put 12oz of 134 back in it b/c it had been leaking with the old fittings. It can't have all gotten used up since then, right?

    that black wire goes into the compressor between the pulley and the body of the compressor, is there anything user-serviceable in there? I'm worried that I yanked something loose on the compressor side of it.

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    You can test if you have leaked refrigerant by jumping the low pressure switch connections. Other than that test you would need a multimeter to trace if a connection got broken.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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    Administrator Ron's Avatar
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    Quote Originally Posted by DaraSue View Post
    I'm having the same issue. #10 fuse is fine. Last fall I accidentally yanked the wire that goes to the compressor loose while trying to take the intake manifold off. It came apart at this junction and I can feel it click into place (I think) when I try to put it back together, but the center of the compressor still doesn't turn.

    20180506_092621_1.jpg

    It's this compressor (r-134), looks kind of the aftermarket one DMCH sells but I don't think it actually is.

    20180506_115024.jpg

    What are the odds that something else just happened to go wrong after I messed with that wire? The A/C was working fine last fall. I haven't used it all that much (probably less than 8 hours total in almost 2 years, mostly for less than 20 minutes at a time if I'm in stop and go traffic, once for a few hours on the way back from Vegas). The compressor was replaced by the seller and the lines were replaced at DMCMW after I bought it (it still had the old R12 fittings). They put 12oz of 134 back in it b/c it had been leaking with the old fittings. It can't have all gotten used up since then, right?

    that black wire goes into the compressor between the pulley and the body of the compressor, is there anything user-serviceable in there? I'm worried that I yanked something loose on the compressor side of it.
    No, it shouldn't use any, ever. Leaks should be the only loss.

    You can check the compressor end by disconnecting its pig tail and jumping it momentarily to the 12V (+) jump post. If it engages, follow the suggestions above to continue. ...probably better to start your own thread to avoid confusion tho.

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    Stupid Newbie DaraSue's Avatar
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    Thanks, guys. I wasn't sure if it would be a greater sin to threadjack or to start another thread about a similar issue.

    Just one more question - if I'm getting current on the wire that comes out of the harness to the compressor, does that mean it's not the low pressure switch cutting it off?

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    Quote Originally Posted by DaraSue View Post
    Thanks, guys. I wasn't sure if it would be a greater sin to threadjack or to start another thread about a similar issue.

    Just one more question - if I'm getting current on the wire that comes out of the harness to the compressor, does that mean it's not the low pressure switch cutting it off?
    Dara,
    With the key on (engine can be off) and the mode selector turned to AC (NORM), you should hear your cooling fans come on and you should have +12 on the wire to the compressor clutch.

    If you do, then check to see if the compressor clutch is engaging. You should hear a "thunk" sound. If not, check that wire connector again that was in your picture. Perhaps it is not completely connected.

    If you do not get cooling fans and there is no power on the compressor wire, jumper the low pressure switch to see if the fans come on and compressor clutch engages. If so, it would indicate low refrigerant.

    Ron

    AC Compressor Circuit.JPG

  6. #6
    Stupid Newbie DaraSue's Avatar
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    Quote Originally Posted by DMC-Ron View Post
    Dara,
    With the key on (engine can be off) and the mode selector turned to AC (NORM), you should hear your cooling fans come on and you should have +12 on the wire to the compressor clutch.

    If you do, then check to see if the compressor clutch is engaging. You should hear a "thunk" sound. If not, check that wire connector again that was in your picture. Perhaps it is not completely connected.

    If you do not get cooling fans and there is no power on the compressor wire, jumper the low pressure switch to see if the fans come on and compressor clutch engages. If so, it would indicate low refrigerant.

    Ron

    AC Compressor Circuit.JPG
    The fans do come on, I don't have my meter with me but the test light comes on if I stick the probe into the switch side of the connector. The clutch just doesn't engage.

    I'll try jumping the compressor end of the wire when I get home and see what happens. It feels like it snaps into place when I connect the ends together but maybe something's broken inside the sheathing.

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    Administrator Ron's Avatar
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    Quote Originally Posted by DaraSue View Post
    Thanks, guys. I wasn't sure if it would be a greater sin to threadjack or to start another thread about a similar issue.

    Just one more question - if I'm getting current on the wire that comes out of the harness to the compressor, does that mean it's not the low pressure switch cutting it off?
    Yes...If you apply 12V to the compressor, regardless of where it comes from (jumper, pink harness wire, etc), the clutch should engage.
    If it does not, it's probably the plug-in connection at the compressor, a bad clutch coil, or a wide clutch plate gap.
    A non stock compressor coil may have a 2nd wire that must be grounded.

  8. #8
    Stupid Newbie DaraSue's Avatar
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    I tried running a store-bought jumper wire (with clips on each end) from the jumper post to the compressor plug and nothing happened, then it finally occurred to me to try sticking the test light where the wire goes into the body of the compressor and it still lit up. So I guess the problem is somewhere further down the line. I'll try and figure out what brand/model it is and how it's supposed to be wired and if I still can't spot anything obvious I guess it's time to take it to the shop.

    Thanks everyone, hopefully some of my flailing with this is useful to Barry too...

  9. #9
    Delorean Guru
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    If you are getting 12 volts at the clutch and it still won't engage, measure the gap. I had one car with too big a gap and it would only engage when cold. Once it warmed up it would not engage again.
    David Teitelbaum

  10. #10
    Administrator Ron's Avatar
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    Quote Originally Posted by DaraSue View Post
    I tried running a store-bought jumper wire (with clips on each end) from the jumper post to the compressor plug and nothing happened, then it finally occurred to me to try sticking the test light where the wire goes into the body of the compressor and it still lit up. So I guess the problem is somewhere further down the line. I'll try and figure out what brand/model it is and how it's supposed to be wired and if I still can't spot anything obvious I guess it's time to take it to the shop.
    Unclear what you meant by "still".
    Anyway, are you saying that, using a jumper wire, you jumped from the battery's jump post to the compressor's pigtail wire plug (right where the pink harness wire plugs in to it) and nothing happened (not even a faint spark), AND, you then disconnected the jumper wire and connected one end of a test light to the battery's jump post and the other end to the compressor's pigtail wire, not where the pink harness wire plugs into it but closer to the compressor (by piercing the insulation with the light's probe maybe)? If so, the first test says power did not get to the compressor coil, and the second test says it did. This sounds like the pig tail wire is broke under the insulation (probably right behind the plug).
    Try connecting the jumper wire to the battery's jumper post and the same place you did with the test light (ie "where the wire goes into the compressor body" instead of the compressor's plug). Be careful, if it has a short and the jumper wire does not have a fuse, it will get HOT fast! If the clutch then engages, splice in a new plug. If not, but it sparks, the coil is weak or the gap is too wide...tap the clutch lightly and see if it engages. Otherwise, you must have done something wrong...

    Hang in there....

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