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  1. #11
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    stephan's Avatar
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    OK Adam, you did try a different relay already? I'm out of ideas then cuz I don't think the module can be disassembled & checked. Besides I think the module is "downhill" of the relay in the power supply order. I would try & find out just where the power is coming from that is supplying the relay when the key is off. Have you had any electrical accessories installed lately? Are you noticing any other electrical gremlins affecting anything else that could be causing this??
    If not, then I would go to the library & photo copy the wiring diagram out of the repair manual for your truck. That way you can see where the wire that is energizing your relay all the time, is connected to along it's path. I think that possibly something is feeding back from another appliance, or it could be a short like you said. Either way you'll need the diagram to figure out where to check.
    New track, I'm looking at a diagram that shows 2 blower motor relays, one for the heater circuit & one for the ac. Same blower motor but wired for both functions through 2 different relays. Is it possible your truck has 2 also? If so you may have replaced the good relay & the bad one is still in the circuit.
    I would get a wiring diagram first thing. It will save you a lot of time & also save money on the wrong parts.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  2. #12
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    I found a wire diagram yesterday and after going over I am 80% sure that the issue lies with the Blower Motor Resistor Assembly (On HVAC module near blower motor). After following the diagram I see that there is a constant power source going through the 40amp fuse under the hood. It then runs to the Blower motor relay in the Blower motor resistor assembly. This relay must be stuck closed and therefore keeping the motor running even when the truck is turned off. Now the only problem that I'm haveing is getting the right part. My assembly seems to be different then the 2 on file that are meant to be for my truck. Even the dealership gave me the wrong part. Tomorrow I will take it out and just bring it in to a parts store in hopes that they can find me what I think I need.

    At least I have heat....but it is very very hot. I drove around yesterday with the sunroof open and windows cracked open while just wearing a T-shirt. It was -25 C.

    Thank You for your help Stephan and I will post back it the fix worked.

  3. #13
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    That's great Adam. The wiring diagram has put you miles ahead in solving this.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  4. #14
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    I found the part on the AC Delco site under the AC Systems heading. It was $104 and it worked like a charm. Thank you for your help I can now control the heat in my truck again.

  5. #15
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    Excellent, glad it fixed it, & thanks for posting back with your results Adam. It's always nice to know how these things turn out.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  6. #16
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    Red Wing, Minnesota, United States
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    As for the squeeling my silverado does it too on the cold mornings, but if I turn the fan off and then back on its fine.
    99 K1500 Suburban LT "THE BEAST"
    Hypertech III, K&N, true dual
    285/75/16
    ___________________________
    Jason

  7. #17

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    I'm a little late to this discussion, but I had the same problem as littlesunny and like to share the solution I found to fellow GM owners...

    My problem was that 3 settings on my climate control switch didn't work (or they would work intermittently and sometimes with a grinding-like sound). I thought it had something to do with the climate control switch itself, or possibly the blower motor and when I took it to the dealership I found out it was a melted blower motor resistor harness. They told me it was going to cost close to $100 for the part, so I went shopping on my own and found a harness that was $33. It was way better than the one the dealership mechanic showed me, which only had black and white wires and seemingly one gauge size. The harness I found matched the one in my 02 Silverado, both wire color and gauge size and now my heat and a/c work perfect. I found the harness at http://www.buywiring.com/7-wire_blow...co_pt2195.html

    They also told me that the resistor tends to need to be replaced, but mine looked ok. Sorry I don't have any helpful information for the resistor...

    Hope this helps!!!!

    GM Forever.

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