Usually is a vacuum problem. The vacuum works through the climate controls to make the vent doors open and close.
My 2000 suburban for is blue and he added the AC on both sides
can you please clarify what you mean, do you mean that the front heater blows cold but the rear blows hot or do you mean that when the heating is on cold it blows hot? many thanks paul
check to see if the controls for the vents are working, there is ususally a vaccum control unit and it may mot be working on the rear vents. hope it helps. duboff
You will need to replace the rear expansion block valve and the recharge the system with freon and oil..............
Possible blockage in the rear air units expansion valve. I just replaced mine for the same reason.
I believe the upper vents are for A/C only. The floor vents are for the Hot air. Test your ceiling controls by moving the knob from cold to hot, you should hear the air pass from upper vents to lower vents. Providing of course you have selected REAR from the front control panel.
You will have a bad rear expansion valve located in the rear a/c unit.........
Your front blower motor has gone out. There is a front and a rear blower motor.
the accuator, located in the rear passenger side is bad. the controls in front when turned go to an accuator in the rear there are two of them one for hot/cold and one for the vents.
Front heater core is in the dash, the rear heater core is all the way in the back of the vehicle. If you have steam coming out of the dash vents, the front HC is leaking. If you have steam coming out of the rear heater vents, then the rear core is leaking.
Most likely the rear expansion tube or valve is defective.
The temperature settings on the rear vents are the same as the front vents on the same side of the vehicle. Ensure they are on heat, turned on, and are set to blow out the top (not toward the passenger's feet).
Start with flushing both heater cores. The rear one may be plugged with crud.