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'91 K5 blowing AC/fan fuse

Discussion in 'The Garage' started by 91K5, Apr 23, 2006.

  1. 91K5

    91K5 1/2 ton status

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    The other day my K5 popped the fuse that runs the AC/heater fan system, and I'm at a loss as to where to start looking, when I stuck a new fuse in the first time, the fan ran for a second then blew the fuse, now it just poppes them as soon as the fan is turned on. Also the parking brake light comes on when the fuse blows, maybe this fuse runs part of the ABS or something else?

    Any ideas would be much appreciated, it's getting hot here :(
     
  2. JEBSR

    JEBSR 1/2 ton status

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    Unplug the fan motor and replace the fuse, if the fuse doesn't blow any longer then replace the motor. This is a common problem when the motor takes a dump.
     
  3. 91K5

    91K5 1/2 ton status

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    Tried it with the fan unplugged, no dice, still pops them.

    Could it possibly be the fan dash switch? Is there any way for it to short to ground? Been a while since I've had the dash off and messed with that part.
     
  4. JEBSR

    JEBSR 1/2 ton status

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    anything is possible, however I would get a wiring diagram and find everything that the fuse powers and start unpluging the items one at a time and see if I could find it that way. It could very possibly be in the wiring but more times than not it is a componant and not the wiring.
     
  5. 91K5

    91K5 1/2 ton status

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    OK I pulled the dash apart and removed the fan switch, and it still blows the fuse when you switch the HVAC from off to anything else. Does anyone have a wiring diagram for this or can tell me what all runs off that circuit?
     
  6. 91K5

    91K5 1/2 ton status

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    ttt, anyone have a better diagram than the haynes manual, or other ideas?
     
  7. cbbr

    cbbr 1 ton status GMOTM Winner

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    Which diagram are you looking for? Dash, blower motor, .....?
     
  8. 91K5

    91K5 1/2 ton status

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    Whatever I can find that is part of that AC circuit. Dash would definately be helpfull though.
     
  9. HarryH3

    HarryH3 1 ton status Author

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    Unplug the blower relay and see if the fuse still blows. It's on the a/c box under the hood, not too far from the blower motor. If it's shorted internally then it will pop the fuse.
     
  10. 91K5

    91K5 1/2 ton status

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    OK guys, I found the culprit. It's the switch that goes into the accumulator tank, facing towards the pass. side, with two green (light and dark) wires coming off of it. Now the question is which switch is this (clutch cycling switch?) and if I take it out is it going to leak the refrigerant out?
     
    Last edited: Apr 24, 2006
  11. 91K5

    91K5 1/2 ton status

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  12. cbbr

    cbbr 1 ton status GMOTM Winner

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    That's a pressure switch, right?
     
  13. HarryH3

    HarryH3 1 ton status Author

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    You can unscrew it without losing refrigerant. There's a schrader valve in the accumulator.

    Are you sure that the switch itself is bad? It just passes power to the compressor clutch. Unplugging it will take the clutch out of the power loop. If you connect the two wires that go to the switch together, the a/c should run. If the fuse still blows, then the switch is good. :(

    You can also connect an ohm meter to each pin on the switch (while it's still installed) and take a reading from each pin to ground. It should be an open circuit, if not, then the switch has shorted internally.
     
  14. 91K5

    91K5 1/2 ton status

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    I'm pretty sure it's the switch, as I had everything under the hood unplugged (fan, resistor, relay, compressor clutch) except that switch and it still blew the fuse, as soon as I unplugged that part the fuse stopped blowing. I will try to jump that connector and verify it's that switch this afternoon.

    So if it is this switch, it's the A/C compressor clutch switch right?
     
  15. 91K5

    91K5 1/2 ton status

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    OK tried seeing if that switch was short to ground, and doesn't appear to be. Now I'm really stumped, as long as that switch isn't plugged in, it won't blow the fuse, but the switch isn't shorted which would cause it. All the wiring appears to be in good shape, and i'd think if it was the wire it wouldn't care if it was plugged in or not it'd still have a short in it.

    Anyone got a wiring diagram for this sucker?
     
  16. opfor2

    opfor2 1/2 ton status

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    It could also be the AC compressor clutch. Something is grounding out. I would check all of your ac/heater wiring. If you removed the two wires from the hi pressure switch and the fuse didn't blow then I would go from there. You definitely have a short in the wiring harness.

    Dan..
     
  17. 91K5

    91K5 1/2 ton status

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    Is there another relay somewhere just for the A/C? I know theres one on the A/C box near the fan and resister, but parts houses show two relays, one for heat and one for A/C.

    What gets me is with that cut off switch on the accumulator unplugged, the system works, albeit the compressor won't engage for AC, but I have a working fan, heat, vents, def, etc.
     
  18. opfor2

    opfor2 1/2 ton status

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    Well then it looks like you've narrowed it down. Trace the wires from the pressure switch to the compressor clutch. The AC clutch could be shorted out.
     
  19. 91K5

    91K5 1/2 ton status

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    Now it gets even more interesting. I stuck a paper clip into that harness to the accumulator cut off switch, bypassing it, and the AC turns on, clutch engages, fan blows, everything works fine for a minute and then blows the fuse.

    So now, with that cut off switch completely disconnected, everything works fine (tho compressor wont engage obviously) and will not blow a fuse. With that switch connected it blows the fuse almost instantly. With that switch bypassed with a jumper, it blows the fuse after a minute or so. This gets more confusing the more things I try. :rolleyes: At this point I'm starting to think it has something to do with the A/C relay, but where is it? The one on the A/C box is just for the heater right?
     

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