The front vents blow at floor and dash but not defrost. I have tried the relearn on your forum which will start blowing full force at windshield but after 30 sec goes back to floor and will not adjust back to windshield. I have pulled the battery which gives defrost then back to floor. The fans work fine and adjust temps and speeds but cannot get the defrost to stay. Please help

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ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#13027 Closed 2010 Gmc Acadia public

Sparky,
The throttle position sensor was replaced and since then hvac will blow floor and vents but not defrost. I have tried the relearn from your thread which gives full defrost for 30sec then back to floor and vents. Defrost will only work after the relearn procedure for that short time. Everything was fine until the engine code was reset from the TPS. I have place controls on auto and after restarting, auto is not lit.

Everything was working fine, then right after the engine code was reset, the vent controls became unresponsive

Sparky

Chances are that when the TPS was replaced that the battery was either disconnected or all codes were cleared from all modules with a scan tool to verify the repair.

If the battery was disconnected  or the HVAC codes were also cleared after the repair and the HVAC system adjusted before the recalibration was finished the doors will not function properly.

Assuming that your have recalibrated the system correctly and the mode door actuator is still acting up, chances are that the mode door actuator itself is faulty and will need to be replaced.

Important:  Do not adjust any controls on the HVAC control module while the HVAC control module is self-calibrating. If interrupted, improper HVAC performance will result.

  1. Remove the HVAC/ECAS fuse for a minimum of 10 seconds.
  2. Install the HVAC/ECAS fuse.
  3. Start the vehicle.
  4. Wait 40 seconds for the HVAC control module to self-calibrate.
  5. Turn the ignition off for at least 10 seconds but no more than thirty seconds.
  6. Restart the engine and check operation of the HVAC system.

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