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John, GMC Technician
Category: GM
Satisfied Customers: 9176
Experience:  ASE MASTER TECHNICIAN/40 years experience
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2001 Yukon: heater blows..cold air..the control module..coolant

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I have a 2001 Yukon XL and the front heater blows cool/cold air. I have replaced the thermostat, reset the battery, replaced the control module and replaced the coolant. The funny thing is the back heater works just fine. Any suggestions?


Your problem most likely is a faulty air temperature actuator,but first make sure both heater hoses going into the front of the vehicle are hot (if not,possible restricted heater core).Here is some info to help you.

Temperature Valve Actuator Replacement

Removal Procedure

  1. Remove the instrument panel hush panel .
    Object Number: 372310  Size: SH

  2. Disconnect the electrical connector (8) from the air temperature actuator (9).
    Object Number: 363779  Size: SH

  3. Remove the air temperature actuator retaining screws.
    Object Number: 363780  Size: SH

  4. Remove the air temperature actuator.

Installation Procedure

    Object Number: 363780  Size: SH

  1. Install the air temperature actuator.
    Object Number: 363779  Size: SH

    Install the air temperature actuator retaining screws.
  2. Tighten
    Tighten the screws to 1.6 N·m (14 lb in).

    Object Number: 372310  Size: SH

  3. Connect the electrical connector (8) to the air temperature actuator (9).
  4. Install the instrument panel hush panel.
  5. Calibrate the HVAC module actuators.

Actuator Recalibration

The HVAC control module will relearn the actuator limits whenever power is disconnected and re-connected to the module.

Use the following steps to perform the calibration update:

  1. Turn OFF the ignition.
  2. Remove the battery positive voltage circuit fuse of the HVAC Control Module.

    Important: The scan tool must be disconnected from the vehicle to properly perform the calibration procedure. If a scan tool is connected before this procedure is completed, then new calibration values will not be stored.

    Important: Failure to wait 60 seconds will not allow the HVAC control module sufficient time to clear the old calibration values.

  3. Wait 60 seconds.
  4. Install the fuse.
  5. Turn ON the ignition.
  6. Wait 60 seconds before installing a scan tool.
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