2000 GMC Sierra Clut Coil Check

Tiny
CLAY.SPANGENBERG
  • MEMBER
  • 2000 GMC SIERRA
  • V8
  • 2WD
  • AUTOMATIC
  • 135,000 MILES
Hello Everyone, I have a quick question, the A/C in my truck went out a little while ago, and we are hoping to get it working before the heat of the summer hits. We found the belt to the A/C broken after our A/C quit working, we then replaced the belt and it still doesn't work, but we noticed that we are now starting to pop fuses. If we disconnect the plug going into the clutch coil we no longer pop the fuse. I have tried jumping the low pressure switch and that didn't work. You can turn the compressor by hand so that indicates to me that the compressor isn't seized. At the plug to the Coil I am getting 13.00 Volts that is with the low pressure switch bypasses, when the low pressure switch is plugged in I am still getting 13.00 Volts that tells me that my system is still holding a charge.

Are there any other test I could do?

Can I check the Clutch Coil to see if that is what needs to be replaced?

Or would it more likely be the Clutch?

Can I do this without having to have my System evacuated?

Thanks,
Clay
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Friday, June 25th, 2010 AT 1:40 PM

9 Replies

Tiny
CARADIODOC
  • EXPERT
Hi Clay. Welcome to the forum. Blowing fuses doesn't have anything to do with the amount of charge in the system. You already found the clue by unplugging the clutch coil. It is either shorted or grounded. Use an ohm meter to measure between the two clutch coil terminals and from either one to ground. The reading should be infinite to ground, and around 2 - 4 ohms between the terminals. If it tests ok, the short could be intermittent, especially if the fuse doesn't blow right away.

A trick you can use is to fashion some spade terminals and a 12 volt light bulb to plug in in place of the blowing fuse. The bulb will not allow enough current to pass to operate the clutch, but it will provide a dandy indication of a short. The bulb will be full brightness when the short is present and be dim or go out when you do something to remove the short.

The system doesn't have to be discharged to replace the clutch unless you have to remove the compressor for access. Even then, you should be able to get enough flex from the hoses to get the tool in there to pull the clutch off.

Caradiodoc
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Friday, June 25th, 2010 AT 1:56 PM
Tiny
CLAY.SPANGENBERG
  • MEMBER
Thank you CaradioDoc for the Quick Response!

If I run the tests, and I do find that there is 2-4 Ohms then what would be my next step, the A/C doesn't Kick on at all and there is no Click from the clutch, am I on the right track believing that it is the coil, or would I be safer replacing both Clutch and Coil.
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Friday, June 25th, 2010 AT 2:07 PM
Tiny
CARADIODOC
  • EXPERT
The first issue is the blowing fuse. If it is due to the clutch coil, it was turning on, otherwise the fuse wouldn't have blown. There could also be a wire that is grounded. That's where the light bulb trick is handy. The problem is you might have to bypass the compressor relay to power up the circuit so you can do the troubleshooting. I forgot to mention that. You can remove the cover from the relay and squeeze the contact, but I find it easier to remove the relay and stick a paper clip between the two terminals. To find which terminals to jumper, look for one that has 12 volts all the time. Use that one and the one that's kity-corner from it, assuming you have four pins in a square configuration. If two pins have 12 volts, turn the ignition switch off and check again. Only one should have 12 volts then.

Caradiodoc

When the bulb is bright indicating something is shorted, unplug the compressor. If the light stays bright, the short is still there. That means you don't have to spend money on a new clutch but you have to search through the wiring harness to find the short.

Caradiodoc
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Friday, June 25th, 2010 AT 2:23 PM
Tiny
CLAY.SPANGENBERG
  • MEMBER
Sorry to Keep Asking Questions,

But wouldn't unplugging the compressor and not having a short verify that the short is within the coil itself? Sorry if this is completely off, but there is one thing I also forgot to mention, right before the A/C quit the A/C and Recirculation light flashed inside the vehicle, from what I have read it is due to a dirty cabin air filter, I have replaced that filter since then, but would this indicate otherwise in my situation?
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Friday, June 25th, 2010 AT 2:53 PM
Tiny
CARADIODOC
  • EXPERT
Your first sentence is exactly correct, but the problem is if it is intermittent you won't know right way. If the new fuse always blows right away, that means the problem isn't intermittent; it's there all the time. Those problems are a lot easier to find but you risk popping a new fuse every time you put one in. You might waste a lot of fuses by the time you find the problem. On the other hand, if the fuse always blows except when the clutch is unplugged, you can be pretty sure that's the culprit.

I never got involved with cabin air filters. It's interesting that flashing lights can tell you when it needs to be replaced, but that too should not cause blown fuses.

Caradiodoc
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Friday, June 25th, 2010 AT 3:05 PM
Tiny
CLAY.SPANGENBERG
  • MEMBER
Well, my fuse does blow right away, I mean it requires a 20Amp fuse and as a test I installed a 25amp fuse and from the time it takes me to push the button and then go look at the fuse it has already blown, but only when the wire is connected to the compressor, otherwise the fuse will not blow. That is what has led me to believe that their is a short in the clutch/coil itself. =/
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Friday, June 25th, 2010 AT 3:10 PM
Tiny
CARADIODOC
  • EXPERT
Yup. Did you double-check its resistance? I think you found the problem.

Caradiodoc
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Friday, June 25th, 2010 AT 3:16 PM
Tiny
CLAY.SPANGENBERG
  • MEMBER
I will check the resistance when my dad brings the truck home. If the resistance is out of the 2-4 Ohm range that means it's bad correct? But if it is still in the 2-4Ohm Range it is good? And where is the best place for me to get the part other then the dealer because they normally mark the price way up, do you have any online resources you recommend?
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Friday, June 25th, 2010 AT 3:19 PM
Tiny
CARADIODOC
  • EXPERT
The resistance value is just a guesstimate but it's nice to have a second test to verify your findings. Remember to check for a short to ground too, not just a short between the two termials.

These coils have such an extremely low failure rate, I would head to a salvage yard for a good used one. Some yards will only sell the complete compressor. They might have a core return unit you can pull a clutch from. Some yards will remove the clutch from the compressor for you. They might pull your old one off too or they might borrow / rent you the puller. I visted 11 of 16 "Pull-A-Part yards last summer. Pay a buck admission, grab a wheelbarrow, throw your tool box in it, and have fun. Parts are REAL inexpensive. That chain of yards is in Georgia, Alabama, Kentucky, Tennessee, Indianapolis, and other states east of those places. The are kept very clean and well-organized. I got a liftgate and sliding door for my rusty trusty '88 Grand Caravan for arounf 90 bucks for the pair. Similar yards around St. Louis think their parts are made of gold, and they charge accordingly. One guy wanted $250.00 for just the liftgate.

I just checked the price list from Pull-A-Part. An entire compressor sells for $14.35 without a warranty, $18.22 with a warranty, and $5.08 core charge for your old one. Add sales tax and an environmental fee and you're still looking at around 20 bucks, ... Less if you just pull the clutch off.

Caradiodoc
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Friday, June 25th, 2010 AT 3:42 PM

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