Bruce P
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This thread is for informational purposes only, no need to reply unless you want to comment on this subject. I hope
that this troubleshooting procedures will help someone else with the same issue to the HVAC problem I found.
Last summer 2024 my daughters 2002 Yukon would only blow out the Defrost vents, adjusting the Climate Control would not
change anything. She had the Mode Actuator and Climate Control replaced with no success. About a month ago Feb 2025 I
had time to troubleshoot the HVAC problem on her car.
The first thing I performed a Re-calibration of the Actuator & Climate control by the GMC Service Manual Instructions The only Actuator that moved was the Air Mix Actuator located at the Center Floor Module.
I checked the Voltage on Terminal #7 which is ground and Terminal #9 on the Air Mix actuator. Terminal #9 is voltage signal
bac to the Electronic Climate Control. When I checked voltage at different temperature settings see the following.
1: 1.40 Volts at 82deg. setting
2: 3.95 Volts at 65deg. setting
When I checked the Mode Actuator at the same terminals, I got 5.0 volts in defrost mode and 0.0 volts in Panel mode. The problem with this voltage it is outside the calibration mode range. So, to correct the issue when I install a small screw into the Actuator Damper wheel for the defrost travel stop and a stop bracket for the travel for Panel/Dash/Floor Air. I rechecked the voltage on Terminals #7 to #9 voltage as follows.
1: 3.71 Volts in defrost mode.
2: 0.27 Volts in Dash mode.
3: 2.44 Volts in Floor mode.
With the correction to the travel of the Mode Actuator which is the one located above the gas pedal. The HVAC system worked as it should, also the Rec. / Outside damper started working again. I believed the problem developed from the sealing foam on the Defrost Damper and the Dash Damper going bad, which caused the Actuator to travel outside its range. When I turn the HVAC fan on small pieces of foam would come out the defrost onto the top of the dash, the Yukon has 180,000 miles on it.
I also saw a lot of post with basically the same issues, just suggesting a simple voltage check before purchasing parts that were not needed in her car's situation.
This is the first time I saw something like this in working on vehicles for 65 years.
that this troubleshooting procedures will help someone else with the same issue to the HVAC problem I found.
Last summer 2024 my daughters 2002 Yukon would only blow out the Defrost vents, adjusting the Climate Control would not
change anything. She had the Mode Actuator and Climate Control replaced with no success. About a month ago Feb 2025 I
had time to troubleshoot the HVAC problem on her car.
The first thing I performed a Re-calibration of the Actuator & Climate control by the GMC Service Manual Instructions The only Actuator that moved was the Air Mix Actuator located at the Center Floor Module.
I checked the Voltage on Terminal #7 which is ground and Terminal #9 on the Air Mix actuator. Terminal #9 is voltage signal
bac to the Electronic Climate Control. When I checked voltage at different temperature settings see the following.
1: 1.40 Volts at 82deg. setting
2: 3.95 Volts at 65deg. setting
When I checked the Mode Actuator at the same terminals, I got 5.0 volts in defrost mode and 0.0 volts in Panel mode. The problem with this voltage it is outside the calibration mode range. So, to correct the issue when I install a small screw into the Actuator Damper wheel for the defrost travel stop and a stop bracket for the travel for Panel/Dash/Floor Air. I rechecked the voltage on Terminals #7 to #9 voltage as follows.
1: 3.71 Volts in defrost mode.
2: 0.27 Volts in Dash mode.
3: 2.44 Volts in Floor mode.
With the correction to the travel of the Mode Actuator which is the one located above the gas pedal. The HVAC system worked as it should, also the Rec. / Outside damper started working again. I believed the problem developed from the sealing foam on the Defrost Damper and the Dash Damper going bad, which caused the Actuator to travel outside its range. When I turn the HVAC fan on small pieces of foam would come out the defrost onto the top of the dash, the Yukon has 180,000 miles on it.
I also saw a lot of post with basically the same issues, just suggesting a simple voltage check before purchasing parts that were not needed in her car's situation.
This is the first time I saw something like this in working on vehicles for 65 years.
![IMG_5230[1].JPG](/data/attachments/448/448327-63423f124f98ba08db4899cb08e13831.jpg)
