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Thread: AC issue fuse #10 blown

  1. #1
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    AC issue fuse #10 blown

    I attempted to fill and run AC system for first time. The car failed vacuum test so we only loaded about 500g. The compressor came on. It ran for a couple minutes. The high side pressure pegged and then fuse #10 blew. The car has a new high pressure, low pressure, pressure relief, office tube, seals, accumulator and a GM compressor. Is this a high pressure switch wiring issue?

  2. #2
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    If it won't hold a vacuum you had no business putting any refrigerant into it. The next step should have been a nitrogen fill to 200 psi and a leak test. Make sure you have the correct size fuse in #10. If it keeps blowing you have a wiring problem or the clutch on your GM compressor draws too much current. Might have to use a relay. If you "pegged", the high side, the high side pressure switch should have shut the compressor off. The low side pressure switch should not have let the compressor run with only 500 G of refrigerant. You have some work to do. For the high side to "peg" with so little refrigerant, something is VERY wrong. Possible blockage on the output of the compressor. Are you sure you only put 500 G in? Sounds like you put a lot more than that in. if you are using R-12 you only put in 2.2 lbs. If you are using -134 you use about 1 3/4 lbs.
    David Teitelbaum

  3. #3
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    Quote Originally Posted by David T View Post
    If it won't hold a vacuum you had no business putting any refrigerant into it. The next step should have been a nitrogen fill to 200 psi and a leak test. Make sure you have the correct size fuse in #10. If it keeps blowing you have a wiring problem or the clutch on your GM compressor draws too much current. Might have to use a relay. If you "pegged", the high side, the high side pressure switch should have shut the compressor off. The low side pressure switch should not have let the compressor run with only 500 G of refrigerant. You have some work to do. For the high side to "peg" with so little refrigerant, something is VERY wrong. Possible blockage on the output of the compressor. Are you sure you only put 500 G in? Sounds like you put a lot more than that in. if you are using R-12 you only put in 2.2 lbs. If you are using -134 you use about 1 3/4 lbs.
    The car barely failed test. We opted to partial fill to see if the system would work. Hopefully its just a fitting that needs to tightened. I am running 134 refrigerant and 20 amp fuse. I just checked the low side and it is 84 psi. I blew out all the lines with ac line cleaner. Everything blew out, but I wonder about the condenser coil fitting. I am wondering if it kinked when I tightened it. I will check the draw on the compressor. I also have a idle stop solenoid on that circuit. I only have 0.1 voltage drop on that circuit so I don't think it a resistance issue. I need to turn it on and jump the high pressure switch to see if power is cut to compressor.

  4. #4
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    The clutch coil is an inductance so you cannot measure resistance to calculate current draw. A minor leak at negative 15 psi is a huge leak at 100 psi positive. If a fitting leaks, overtightening it won't stop the leak. The joint must be taken apart and figure out why it leaks. The "O" ring is what seals the joint. If it leaks the "O" ring is not sealing because it is cut, out of position, old, or not the right size. First order of business is to get the system leak-tight. Once you are certain it is good then you evacuate to remove all air and moisture and fill with refrigerant. Check current draw on the clutch coil and figure out why the high pressure switch didn't shut the compressor off and why the low pressure switch also didn't shut the compressor off. Pull the plug off each switch and see if the compressor will run.
    David Teitelbaum

  5. #5
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by David T View Post
    The clutch coil is an inductance so you cannot measure resistance to calculate current draw.
    When powered by DC voltage, yes you can measure resistance and calculate current.

    The #10 fuse also powers the blower speed 1 and 2. So one of your loads is drawing to much current or you have a short in the wiring. You also have some capacitors that may be bad and drawing current. Sounds like you need to measure the current of each load to find your problem.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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    If you power the coil you can measure the current directly. I agree, you must find where all of the current is going. I suggested the clutch coil only because you said you do not have the Sanden unit so it is possible the GM unit draws more than the stock Sanden and that's why you are popping fuses. But it can be anything in that circuit from the fan to the resistors to a bad relay or the wiring.
    David Teitelbaum

  7. #7
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    I had a bunch of AC cleaning fluid stuck in the system, orifice tube was in backwards, and the o ring at relief valve was torn. Compressor clutch was pulling 2.6a. Idle stop solenoid was 5a. I'm running a PM106 blower. Power level 2 was 5a, level 3 was 9a and level 4 was 14a. I should have watched the clutch amp draw and pressure before I broke it all down. I guess the question is could the amp draw increase to 15a if pressure spiked?

  8. #8
    Administrator Ron's Avatar
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    No, pressure doesn't affect the amp draw. ...Once the compressor clutch engages, it takes very little to hold it in. Even if the compressor locked due to excessive pressure, the clutch would hold tight while the belt burnt/something broke, without causing the amperage to go up.

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