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Dave Nova
Dave Nova, GMC Technician
Category: GM
Satisfied Customers: 19451
Experience:  ASE Master Certification. GM World Class Certification
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2005 gmc envoy: actuator..any coolant going..heater core..harness

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2005 gmc envoy rear heat inoperative. the actuator which operates the temp door for the rear ac is not working, and there doesn't seem to be any coolant going to the rear heater core. I checked the actuator by plugging it into the harness that operates the actuator for the blend door and it worked fine. I'm not getting any power to operate the temp door actuator. Can you help
If the control module senses a problem with an actuator, it will shut down that actuator. Try disconnecting the battery for 30 seconds, then reconnect the battery. When the key is turned back on, the module will sweep all of the actuators and recalibrate. Do not touch any of the a/c controls during this period of time(about 2 minutes). Watch to see if this actuator sweeps during the recalibration. Let me know what you find.
Customer: replied 7 years ago.

i tried this and after i hooked the battery back up and turned on the key it did sweep the actuator for the rear temp door. After it completed the sweep it stayed in the heat position which is where the temp selection knob was set. However, when i started the vehicle to let it warm up and see if everything was working the rear temp door returned to the cold position. I repeated this process twice with the same results, now what?


By the way the coolant is flowing through the rear heater core. I checked the lines under the rear of the vehicle and they were getting hot

The problem is the feecback from the actuator is out of limits, so the comtrol module is shutting down the actuator. Replacing the actuator will fix your problem.
Customer: replied 7 years ago.
I replaced the actuator and i still have the exact same problem. what now?
Have you tried disconnecting the battery to let the system recalibrate? If not, the trouble code that is stored in the system from the old actuator will prevent the new one from working as well.
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