2001 Chevy Venture No rear heat.

If the front rear heater switch is on the front and you have temp on warm it should be blowing warm or hot air out of the top rear vents not the bottom. The bottom is the return air. Now if you have the rear heat on r the what ever the temp knob is set on is what temp air you get out of the top vents. Now if both temps are set on warm and you still have cold or cool air blowing inside the side panel on the drivers side there is a damper switch which controls the door to make the air temp hot or cold or in between. If this switch goes bad it won't move the damper door. But the side panel has to come off to get to it. Remove the rear seats and pop the panel off it is clipped in just like the front door panels