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Defroster/AC issue/95 K3500

Discussion in 'Chevy Trucks' started by Stan, Feb 2, 2010.

  1. Stan

    Stan Senior Member
    Messages: 579

    Did a search and checked several componets. When I turn the defroster on the ac does not turn on or air does not blow out of the def vent.The componet in question is the actuator to the right of the gas pedal held on with 2 screws. I removed it from the truck and attempted to turn it by hand...seems frozen. Took it apart and all gears are there in good shape. Is this supposed to turn freely?
     
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Did you remove the actuator and check it's movent with the harness plug still connected yet Stan?. Doing so first rules out any linkage/door binding issues right away.


    To verify the actuator is the problem check the wiring functions for it right at the connector plug with a test light. If it all checks out then the actuator is likely dead. Should have three wires. (Be sure the ignition is in the run position and the blower motor is running for these tests).


    Brown- should show voltage
    Black- should show ground
    White- should have varying voltage as the defrost-floor-A/C-vent positions are changed. Actual voltage doesn't matter as long as it has something and it changes as the positions are changed.


    The A/C may not be activating due to an unrelated issue, such as a low charge/leak. But whether it work's or not you should still have defrost air direction.
     
  3. Stan

    Stan Senior Member
    Messages: 579

    Good idea with harness still attached. I'll ck that later today. I did have power @ the brown. When you say varying voltage is it less than 12 volts? I did check movement of the the heater box and turns freely.

    Does power feed to the white wire from the actuator or from the controlls above?
     
  4. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The white should show varying voltage because it's that varying voltage that controls where the actuator moves to. So the white is your signal (control) wire from the heater control panel. Think of it like a light dimmer controlling a light fixture. As you increase or decrease voltage the actuator moves through it's available travel. At at it's maximum the voltage should show battery voltage or a little less.
     
  5. Stan

    Stan Senior Member
    Messages: 579

    Great direction, thanks B
     
  6. Stan

    Stan Senior Member
    Messages: 579

    Finally had a chance to check this out. I have no power at the white. While the test probe was in I worked the controlls and still nothing
     
  7. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    No voltage on the white indicates the HVAC module is defective, or of course the white wire could be broken or have a weak connection at the HVAC module connector plug. So, before I condemned the module I'd pop it out and check continuity on the white wire between the actuator plug and the HVAC plug. You can even re-run your test right at the rear of the module too.
     
  8. Stan

    Stan Senior Member
    Messages: 579

    Ck'd both sides of the plug going to the actuator. Where would the HVAC module be located? Would the module prevent the AC from kicking on as well?
     
  9. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The heater-A/C control panel is the HVAC module. It's just the "technically correct" name and the one you want to be familiar with if replacement is needed. Saves from whacking the parts guy in the head when he can't find a "heater control panel" in his fancy computer. :D
     
  10. Stan

    Stan Senior Member
    Messages: 579

    Out of site out of mind.... I temporarily made the trk into defrost mode by removing the module and cranking the internals. Now that it reached 80 degrees yesterday without AC its time to fix. I installed a working module without sucess. I have fan and temp controll but no power into the module to operate the compressor or anything related to the controll on the far right side.
     
  11. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Do you want to check the pin outs into the module connector for proper power and ground Stan or have you done so already?
     
  12. Stan

    Stan Senior Member
    Messages: 579

    It doesnt appear to have power at the module
     
  13. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    What do you have for wire colors at the module? I need a refresher. :waving:
     
  14. Stan

    Stan Senior Member
    Messages: 579

    black white brown
     
  15. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    That would be at the actuator. I'm under the assumption you were talking about the module since we already established that you had no power (on the white) at the actuator. So do you have it on the white on the rear of the module? Need to check that as I mentioned before as the white may be broken between there and the actuator.
     
  16. Stan

    Stan Senior Member
    Messages: 579

    I may be lost here...correct me if I'm wrong. The actual knob that controlls the def,heater, etc is the hvac module?
    For what its worth when the ac or recirc button is pushed there is nothing.
     
  17. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    That's correct. Have you verified whether you have power on the white wire there? That would be the same signal wire that you found was dead down at the actuator. If it's dead out of the module then something is up with the module or you have a partial supply problem into it.
     
  18. Stan

    Stan Senior Member
    Messages: 579

    That's correct. Have you verified whether you have power on the white wire there
    That would be my next step. If there is power there I'm assuming its the entire module?
     
  19. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    If there's power on the white wire right at the module then the module IS sending the signal out, but it's not making its way to the actuator. thus the wire is broken somewhere in between. However if there's no power even right at the module then the module isn't sending the command out, thus it's defective.

    I'm going to fast forward on an educated hunch and bet the module is defective because it's not uncommon. But check the white wire first regardless.
     
  20. Stan

    Stan Senior Member
    Messages: 579

    Will do, thanks and will get back with findings