I had this same problem, With it running and heat and blower on full blast remove and unplug the rear faceplate for the rear heat.
Unplug for about a min.
Shut off engine.
Cycle the key 5 times.
Plug in the plug to the face plate.
For about a min. nothing will happen no heater no blower.
After the multiplex system refinds its address, the rear heat will then work again.
this worked for my 04 trailblazer.
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When the battery was disconnected, the HVAC system lost its calibration or one of the door actuators is stuck. With truck on, set all HVAC controls and switches to their OFF or CCW positions. Disconnect the battery, wait about 3 minutes, then reconnect. Turn ignition to ON position, doesn't need to be started, and don't touch any of the HVAC controls for about 3 minutes. This should reset the calibration. If this does not work, a mechanic will need to diagnose the problem.
Sounds like there is a broken rear HVAC actuator for the rear HVAC. There should be two of them. One for the mode, one for heat / a/c control.
Pull the trim panels in the rear and when it's making noise feel the actuators. You should be able to feel the one that is making the noise. The next step woul be to remove it and make sure the door it controls moves freely. It it doesn't you have bigger problem. If it does replace the actuator and you should be good as new.
Let me know if you have any questions and I'll do my best to answer them. Thank you for using FixYa.com!
Hi Jeff. I had the same problem, along with others on my 03 Denali. Along with not blowing hot air from the rear heating system, I had hot air blowing out of the passenger side and cold air out of the drivers' side vents. My battery would go low and had the same smell. I took my Denali in to the dealer and they found it was a bad Fan Control Module. They replace it and everything worked well after. It cost me $293 for parts and labor. Hope this helps.
this fuse controls a few things i will list them and send a copy for you.this way you can determine which asc come on this truck, but i know some do and they are needed,it controls the hvac system (heating/ ac), electronic suspension, rear wheel steering,and heated seats. instead of removing the fuse which cant be done look under the rear seats and unplug the heated seats module theres two one under each seat in the rear seats that will shut it down. hope this helps
You probably have a bad air temperature actuator for the left side.If you can get the codes for the HVAC system it might show up there.Sometimes if you tap the actuator it will start to work.I t is located about the middle of the lower dash area.You might be able to see it from the right side of the console looking up into the lower dash area.If you don`t know what to look for it could be difficult to see.Good luck.
Here is a TSB (Technical Service Bulletin) for your vehicle for loss of temp control. File In Section: 01 - HVAC Bulletin No.: 01-01-39-007 TECHNICAL Subject: Loss Of HVAC System Mode and/or Temperature Control
(Reroute Wiring Harness)
1999-2002 Chevrolet and GMC C/K Pickup Models (Silverado and Sierra) 1999-2002 Chevrolet and GMC C/K Utility Models (Avalanche, Suburban, Tahoe, Yukon, Yukon XL, Denali) 2001 GMC Sierra C3
2002 GMC Sierra Denali
2002 Cadillac Escalade, Escalade EXT
Some customers may comment that they cannot control the HVAC system modes and/or the temperature. These concerns may be intermittent.
There may be poor terminal contact and/or bent terminals in connectors C206 (RPO C68 automatic HVAC controls) or C296 (RPO C60 manual HVAC controls). Excessive tension on the wires due to the wiring harness being miss routed in the instrument panel carrier may cause these conditions.
If the warranty campaign is over i am sure they can or may have in the system on how to correct the problem.
Good luck and hope this helps, keep me posted if you need help on to the repair procedure.
does front air work properly? for heat i mean?.. the blend doors are suspect as well as the heater hoses to the rear core and its heater valve.. possibily the control head is to blame or?, but i cant tell from here