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

  1. #11
    Senior Member Bitsyncmaster's Avatar
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    Often if a meter or test light works and the load does not it points to a marginal connection because the load draws more current than the test loads.

    But as Ron suggested a jumper from the battery jump terminal to the wire at the compressor clutch would show if the connection from the bulkhead to compressor were bad.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  2. #12
    Stupid Newbie DaraSue's Avatar
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    Yeah, I clipped one end of the jumper wire to the battery jump-start post and the other end to the pigtail plug (this one) 20180507_094959.jpg and nothing happened. The motor was off at the time, was it supposed to be on? I had unplugged it from where it connected to the harness and connected the jumper clip to the metal part at the end of the black wire.

    When I used the test light I was putting the probe at the other end of that wire, between the pulley and the body of the compressor, where the arrow is pointing here except further in: 20180507_091726_2.jpg The probe was skinny enough to fit into that space and touch where there was a gap at the end of the sheathing but the clip on the jumper wire won't fit down in there so I'd have to strip the sheathing off farther up to try jumping it again between the plug and the compressor, I guess?

    I also tried running a ground jumper wire between one of the bolts on the compressor and the ground loop on the engine block, and that didn't help, either.

    The gap between the clutch and the pully might be another thing, though. I noticed upon closer inspection that it fits really tight on top but has more space on the bottom, that's not right, is it? Not sure how well it shows up in this pic but it looked like around 1mm on the bottom. 20180507_095132.jpg 20180507_095150.jpg

    I asked the guy who sold me the car where it was from, he thought DPI but it doesn't look quite like the ones on their website. It has the number "B508SC02N" stamped on it but Google only returns a couple of Russian wholesale sites when I search for that. Probably not a good sign...

  3. #13
    EFI'd dn010's Avatar
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    If you applied +12VDC from the jumper post or even the battery to rule out a bad jumper post connection and the clutch did not engage, then you've got issues with the clutch itself and not the wiring. The compressor looks quite new, perhaps the wire going in is broken? You'd need to pull the pulley/clutch off the compressor which is a PITA installed on the car but can be done if you have the tools/puller.

    Before you get into all that, though, I'd hook up the +12V to the compressor connector and jump post, connect the test probe to ground somewhere and then probe the wire lower towards the pulley and see if the probe lights up. Be careful though, there is a lot of ground that the jumper can short out on being connected to the compressor connector. Wrap it up in a cloth or put a piece of cardboard etc between the jumped connector and compressor. The engine does NOT need to be running, nor does ignition need to be in for this, if you jump it from the jump terminal on side of the car by the bulkhead connectors. With any luck, maybe it is just a bad crimp on the connector which would be the easiest fix.
    Last edited by dn010; 05-07-2018 at 03:11 PM.
    -----Dan B.

  4. #14
    Delorean Guru
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    For more info on the gap refer to N:10:08-:09 in your Workshop Manual. To verify if the coil for the clutch is any good apply 12 volts and see what the amps are or try to measure the resistance of the coil without power. if it doesn't draw any amps or you get infinite resistance the coil is bad or not connected at both ends.
    David Teitelbaum

  5. #15
    Administrator Ron's Avatar
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    Quote Originally Posted by DaraSue View Post
    Yeah, I clipped one end of the jumper wire to the battery jump-start post and the other end to the pigtail plug (this one) 20180507_094959.jpg and nothing happened. The motor was off at the time, was it supposed to be on?
    No...it doesn't matter.

    Quote Originally Posted by DaraSue View Post
    When I used the test light I was putting the probe at the other end of that wire, between the pulley and the body of the compressor, where the arrow is pointing here except further in: 20180507_091726_2.jpg The probe was skinny enough to fit into that space and touch where there was a gap at the end of the sheathing but the clip on the jumper wire won't fit down in there so I'd have to strip the sheathing off farther up to try jumping it again between the plug and the compressor, I guess?
    Yes.
    You might try piercing the insulation with something sharp an inch behind the plug and jumping 12V to it first (your probe, a large needle?).
    If that didn't work, a stiff wire with the insulation stripped off of the very end might allow you to carefully reach in where you had the probe end...

    Quote Originally Posted by DaraSue View Post
    I also tried running a ground jumper wire between one of the bolts on the compressor and the ground loop on the engine block, and that didn't help, either.
    The engine is grounding the compressor body...

    Quote Originally Posted by DaraSue View Post
    The gap between the clutch and the pully might be another thing, though. I noticed upon closer inspection that it fits really tight on top but has more space on the bottom, that's not right, is it? Not sure how well it shows up in this pic but it looked like around 1mm on the bottom. 20180507_095132.jpg 20180507_095150.jpg
    The gap wouldn't cause the two tests to differ -- I'd work on that first...

  6. #16
    Stupid Newbie DaraSue's Avatar
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    I tried sticking a t-pin a couple places along the compressor wire and jumping to that (I had to use a length of 12-gauge wire for the one where it went into the compressor because the jumper wire was too short) and still, nothing. It doesn't spark or even seem to get hot. What am I doing wrong? Should I pull one of my other cars up and try to jump straight from the battery? The test light shows current when jumpers are connected or when I connect it to the jumper post.

    Also what does this ground wire do? It comes out of the harness and forks off from the same place as the a/c wire. I remember disconnecting it while working on the intake and it looks a little frayed at the connector.20180508_100657.jpg (It's normally attached, I just unplugged it to try and tighten the bolt.)

  7. #17
    EFI'd dn010's Avatar
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    That's the oil pressure sensor.

    Anyway, if you attach the connector to +12VDC and then probe the wire with a tester connected to ground further down the line near the clutch, that will tell you if you're even getting power in the wire. If you do see power, then you know you have an issue inside. If you just try to apply 12V to the wire down the line, you still can't confirm that the wire is actually getting power or your're piercing the insulation unless you hook the test probe to the connector at the end and see it light up when you apply power down the wire.
    Last edited by dn010; 05-08-2018 at 03:52 PM.
    -----Dan B.

  8. #18
    Senior Member
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    its just a bad clutch coil. its just a electro magnet that grounds through the mounting bolts for the compressor and gets its power through that single wire. you have given it everything needed to energize. the coil can be changed with a special puller. I have done this without taking the compressor out but you need the tools. depending on the compressor vendor these coils will go out often. darn junk parts.

    you might get crafty and hold the plate and take the center nut loose. then use prying devices to pull the plate off. then a snap ring holds the coil on. usually this won't work without bending the clutch plate.

    check the resistance between the power wire and the compressor case. most likely its open. I would have to check troubleshooting but it shouldn't be open. Sarah @ DMC will know the answer.

    Buying a new compressor from dmc is fast and easy.

    Sent from my SM-G950U using Tapatalk

  9. #19
    EFI'd dn010's Avatar
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    AC Clutch Don't Engage With 12V Jumped To Pigtail

    ... or you can diagnose before blowing $250. Itís really not that bad taking it apart IF you have some tools to do so as I already stated. I even have two compressor worth or parts if you need a working coil.


    Sent from my iPhone using Tapatalk
    Last edited by dn010; 05-08-2018 at 09:51 PM.
    -----Dan B.

  10. #20
    Administrator Ron's Avatar
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    Quote Originally Posted by DaraSue View Post
    I tried sticking a t-pin a couple places along the compressor wire and jumping to that (I had to use a length of 12-gauge wire for the one where it went into the compressor because the jumper wire was too short) and still, nothing. It doesn't spark or even seem to get hot. What am I doing wrong? Should I pull one of my other cars up and try to jump straight from the battery?
    Sounds like you did everything right. If you are 100% sure you had a good 12V on the metal part inside the wire (near the red arrow in the pic), the clutch coil needs to come off to find the problem.
    Quote Originally Posted by DaraSue View Post
    Also what does this ground wire do?
    Not really a ground wire, fwiw...It is grounded by the Oil Warning Lamp Sender, which grounds the bulb. (The pressure sender is on the opposite side of the block.)

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