I have a 2004 chevy tahoe 5.3 v-8 new body style. The problem started about a year ago when the front a/c would work but the back a/c would blow heat. I reset the hvac fuse and unplugged the battery. That fixed the a/c where it now blows cold air in the whole car but now the heater blows cold air. I flushed out the heater core, replaced the front blend door actuator and I don't think the thermostat is bad because it runs at normal operating temperature. Does anyone know what the problem could be?

 

I have a 2004 Chevy Tahoe and it was the Resistor. I took it out and it looked burnt up. It got to the point to where the a/c wouldn't blow any air whatsoever. start there its a easy fix.

 

Are you saying no heat both front and back or only a rear problem? If fan operating normally probably not resistor problem