I resolved the non-operable HVAC on our 03 Suburban today. I disconnected the battery for approximately 1 hour while I was doing another task. I reconnected the battery and when I started the truck the HVAC powered up. I suspect that replacing the battery several days earlier caused a voltage spike that messed up the ECM that controls the HVAC. Discounting the battery evidently reset the ECM data stream that activates the HVAC.
I had checked ebay the previous day and saw new AC Delco HVAC units listed for $125 including shipping. I viewed a utube video that demonstrated how to replace the HVAC, which is pretty easy and I was getting ready to do just that, but thought I would give it one last try by disconnecting and then reconnecting the battery which proved successful.
I am wondering how may Tahoe, Yukon and Suburban owners experienced this same failure, then disconnected the battery and replaced the HVAC unit and it worked, no knowing that it might have been all they needed to do is disconnect and then reconnect the battery after a delay of maybe 10 minutes to reset the ECM..
