03 Tahoe heat works only at 90

93redzj

93redzj

Well-Known Member
Joined
Aug 29, 2005
Location
Albemarle
Tahoe has dual climate control, I’ve replaced the control unit used to adjust heat setting, actuator on passenger side under dash replaced last year, and I’m currently fighting the one under dash on driver side which controls where the air flows, through vents, floor, defrost.

The issue now is, the heat will only work when the temp is turned up all the way to 90. If you set it to 89, it alternates between warm/cool air. I’ve tried searching around and came across a fix with inside air temp sensor located above driver head in headliner, changed that and still not fixed.

Heat/AC works on both passenger and driver side, rear works too. Just the heat only blows consistently hot at 90, any other degree setting and it’ll get cool/cold for a few minutes then warm up, then repeat

Any suggestions?
 
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My guess would have been the temp sensor, but you've already changed it. I'm not sure if there's any way to see what the temp sensor is reporting? You could have gotten a bad one out of the box.

My wife's 2005 will switch from heat to air when the outside temp is very close to the set temperature. Does your outside temp on the mirror read correctly?
 
LBarr2002 said:
My guess would have been the temp sensor, but you've already changed it. I'm not sure if there's any way to see what the temp sensor is reporting? You could have gotten a bad one out of the box.

My wife's 2005 will switch from heat to air when the outside temp is very close to the set temperature. Does your outside temp on the mirror read correctly?
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As far as I know it does, but now that you mention it, the display in the rear view mirror that shows temp and direction, does “glitch” from time to time. But not often

I also never have it set to “auto” if that would make a difference in this case. I always have it on either heat or AC with a set temp
 
Sounds like the classic blend door decalibration of that era
 
Ron said:
Sounds like the classic blend door decalibration of that era
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When mine have failed, they've gone full hot all the time. He could run the recalibration and see what happens though.

Reset it by turning the ignition off, removing the HVAC/ECAS fuse (for 1-2 minutes), then reinstalling it and starting the vehicle, allowing the system to self-calibrate for about 40 seconds.
Here's a more detailed breakdown of the process:
1. Turn off the vehicle: Ensure the engine is off, and the ignition switch is in the "off" position.
2. Remove the HVAC/ECAS fuse: Locate the HVAC/ECAS fuse in the under-hood fuse panel (it might be marked HVAC or ACAS).
3. Wait: Remove the fuse for at least 1-2 minutes. This allows the HVAC control module to reset.
4. Reinsert the fuse: Once the timer is up, reinstall the HVAC/ECAS fuse.
5. Start the vehicle: Start your vehicle and let it run for a few minutes.
6. Wait for the calibration: Allow the vehicle to idle for about 40 seconds, while the HVAC control module recalibrates itself.
7. Check for DTC's: Make sure to verify that no DTC's have been set as current DTCs
If the problem persists, it might be a faulty blend door actuator: If resetting the system doesn't resolve the issue, a failing or damaged blend door actuator may be to blame.
 
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