08 Tahoe HVAC Issue. no heat unless 90

[akbrener]

I tried searching here and google, not sure if I am using wrong key words, but seems I am having an isolated issue with both front and rear HVAC units not getting warm. Seen plenty of posts about blend doors for driver/pass side or actuators out of range..

I do not have any issues with any vents not working, driver and passenger side are identical. First cold day the other morning and I noticed that at 80, it blows the same temp as 70. The only way I get hot air out of the vents on the front unit AND rear unit is if I max it out to 90* and it gets toasty.

Both rubber hoses and associated metal pipes that go to the heater cores are hot, engine is running at full normal operating temp. I dropped the black plastic cover under the dash and I think I found the temperature actuator, (lowest one near the center console on pass. side) it rotates when temperature is changed, and the notch is within the 2 marks.

I had this issue last year and was able to get heat functioning properly after running the engine for a while with the cap off the coolant resivoir and adding a bit of water, but no luck this year.

Curious if there is something I am missing, like an internal flap that the actuator should be moving that may be stuck??

AC blows cold no issues there, seems to be isolated to the heater core, and thinking it may be something simple since both units are acting funny.

Thanks

 

[jrobie79]

I have the same issue on my 2011 escalade. following for answers

 

[Kraig]

You found the temp actuator and it rotates, but is it actually moving the door?

 

[akbrener]

You found the temp actuator and it rotates, but is it actually moving the door?

That's what I think I may need to figure out, is the door something that can be seen or moved by hand without tearing into it too far to check that it's open or closed or maybe binding?

 

[Kraig]

Take the actuator off and you should be able to move the shaft by hand. Make sure the shaft and the door are still solidly one piece

 

[Doubeleive]

I had replaced my hvac control and had a similar problem, it worked fine all summer until it came time for heat then it would only give heat to the rear if it was set 89/90 otherwise it would go to cold, after a lot of troubleshooting it turned out the hvac control needed to be reprogrammed for my truck, after that it has worked fine

 

[akbrener]

any reason that the problem is identical with front and rear AC? was able to visibly see the actuators move with temperature increase on the bottom and top actuators for the front HVAC. Rear also wil not blow hot until 90 is selected.. I have about a month or so to figure this out, gonna be a rough winter.

All funtions appear to work, defrost, floor, passenger/driver are independent.

I assume that if the actual flap inside the unit is faulty it all has to come out and be disassembled?

 

[jrobie79]

I had replaced my hvac control and had a similar problem, it worked fine all summer until it came time for heat then it would only give heat to the rear if it was set 89/90 otherwise it would go to cold, after a lot of troubleshooting it turned out the hvac control needed to be reprogrammed for my truck, after that it has worked fine

Did you have to take it to the dealer to be reprogrammed?

 

[Doubeleive]

Did you have to take it to the dealer to be reprogrammed?

yes I did, I had a tech2 but had not done any programming with it at that point

 

[JeepTahoe]

Following for similar issue in 2007 Suburban LTZ. Only heat in front is when temp is at 90 degree setting.

My front controls: 90 degree setting gets hot heat. Anything less is cool/cold.

I just messed around with rear controls, and they appear to be working as they should. Temp changes as you move temp control up an down.

However, after messing with rear controls, the front temp controls seem to be working again so that at the 84 degree setting on the front control I'm actually now getting warm (not blazing hot like at 90) air.

It's got me baffled. I've seen the whole recalibration procedure mentioned but have not tried it yet.