2005 tahoe cannot change rear heat temp...out of ideas

[Jonathan Davis]

I just bought the Tahoe and the heat in the back will not work when trying to adjust it. Here are the steps I've done so far...

1) I replaced the control module, still no change.
2) I removed and recentered the actuator, did a HVAC reset and stil no change.
3) I checked voltage on the vent door actuator and I can see the range from 5v-1v which I do not see on the heat adjustor. I only see a constant 5v. When I do reset the actuator rolls to side and then bottoms out on the heat side.
4) I replaced the HVAC control switch (on the head liner) and still no love.
5) had the system scanned for b codes and nothing was noted about the HVAC.

 

[JR79]

1. Disconnect the battery for about a minute.
2. Reconnect battery
3. Turn the ignition to the ON position for at 1-2 minutes. This is the ON position or first position, NOT the RUN position or second position (I made this mistake). On the ON position, the HVAC systemshould not turn on. So it does not matter if you left HVAC system on front or rear.
4. Turn the ignition to the OFF position for at least 10 seconds. Key can stay in the ignition.
5. Start the engine and confirm the actuators are working correctly by turning the climate knob from cold to hot and from low air, mixed, and high.
6. Have yourself a nice cold beer while the wife praises your status as mechanical genius. (This laststep is critical so don't skip it!)
This was posted by Red Rider. I just finished this project on my 2005 tahoe. Hope it helps.

 

[Jonathan Davis]

Yeah I tried that exact process and a different one I saw in the forums. The only time the heat actuator moves is during the initial power on, it goes from center to 100 and then bottoms out past zero. The only thing I can think of is the actuator is bad some how....

 

[JR79]

Yeah I tried that exact process and a different one I saw in the forums. The only time the heat actuator moves is during the initial power on, it goes from center to 100 and then bottoms out past zero. The only thing I can think of is the actuator is bad some how....

Have you checked the heater line running to the heater core to make sure it's hot ? If you can take the actuator off and manually open the blend door , and the vents blow hot air , it could be an actuator I guess. Maybe a guru will stop by and offer some solid advice. Try switching the front actuator with the rear actuator. If the rear is bad, this should tell you. Good luck.

 

[Jonathan Davis]

yeah i can manually adjust the heat when i remove the actuator, ill try swapping the 2 and seeing if anything changes

 

[Jonathan Davis]

Well it looks like its off to the dealer cause I'm stumped. I was able to put voltage to the actuator and I can get the motor to run only to one side (bad actuator right?) So I bit the bullet and bought an actuator and same symptoms, it runs all the way to the right and then just bottomed out on the left. I'm out of things to check, it seems like its not getting the correct signals and without a scanner my shade tree skills are about tapped out

 

[JR79]

Johnathon- sorry for the late post. From what I understand from reading other posts when fixing mine, when the actuator goes all the way to the right , it is in default mode. Mine did this. After I installed new control module, it did the same thing yours did. I had to take the actuator off and reset the knob to the middle mark ( or anywhere in between two outer marks) , then reset computer. You've probably already gone to dealer by now. I just saw your latest post. Good luck

 

[Jonathan Davis]

actually after digging around i figured out the issue was the rear audio/havc control unit that sits in the back of the center console. It was sending signal even when it was off to the back controller. Which makes sense that when i would reset the rear HVAC that the actuator would run to one side and then bottom out because it was getting constant signal voltage the entire time. I popped the wire harness off the rear audio/hvac unit and the rear temp can be adjusted now. It was literally the last thing i would have thought cause its my understanding that the rear unit only controls the temp when the headliner controls are set to aux. But its fixed, and the dealer got none of my money lol so in the end it all worked out. Thanks everyone for their help.

 

[Joshuasvt]

I may have to try this tomorrow as my rear heat isn't working. Thanks

 

[a4edwin]

I tried unplugging the a/c radio module in the console and I lost all audio in the rear and it still didn't solve the problem for me