2006 heating issue
 

My wifes 06 impala (6 cylinder) doesnt blow heat when idling although it works fine when on the road. Of course my thinking went right to the thermostat which I just replaced with no change in the situation. The blower fan works fine and the coolant level is right where is should be. Could there possibly be a sensor involved in the coolant circuit going to the heater core???
Im confused and any help will be appreciated.
Fred

Is it set for the floor, or a/c vents (upper)?

changing the vents doesn't affect this at all. still blows cold when stopped and hot when moving.

Possible blower motor resistor
 

If i'm not mistaken, the blower motor resistor (located next to the blower motor on the left side) has several sensors in it. Either way, it fixed the heat situation in my wife's 04 Impala. Some people call this a relay. It can be bought on line fairly cheap. Might be worth a try.