Chrysler Repair: 2001 Sebring Heating Problem, coolant temp, temp gauge

Question
My 2001 Sebring's heating system is strange. When it is cold outside (below 40), the heat will usually work. However, the air that blows will cool down when I am idling and heat back up when I push the gas. Is it just the thermostat that needs replacing?

Answer
Hi Fran,
If the thermostat were the cause you would notice it as an overall decrease in the reading of the temperature on the dash (if you have a temp gauge). When you say "push on the gas" do you mean just increase the idle rpm while at rest, or that you are driving in motion? Usually the temp response would be the reverse of that, i.e., the temp would rise when you are at idle and cool down when you are in motion or revving the engine as that increases the rate of pumping coolant and also the air passing thru the radiator increases, both of which lower the coolant temp. to the point where the thermostat would begin to close down the flow of coolant in order to keep a good operating temp.  
On the other hand if the thermostat were stuck open then it could cause what you are experiencing, but then too I would expect it to just run cool generally whether you were idling or in motion, although it might be the case that it would be warmer when you are revving the engine simply because the engine is producing more heat. If you don't have a temp gauge on the car then touch the radiator and see if it feels quite warm or not. It should reach about 190 degrees, which would be something noticeable with a quick touch on its surface. If it seems to be running cool all the time then the thermostat maybe stuck open.
If the coolant temp/radiator seem hot, then I would suspect a problem with the control over the position of the blend air door in the heating box under the dash, possibly due to a voltage regulation issue. Do you notice a warning light for the battery voltage level when you are idling? The temp of the air is controlled electrically on some models by means of an electrically operated door that controlls whether the incoming air flows more or less over the heater core as compared to the core for the ac system.
Please let me know which type of Sebring you have, and whether it might have a digital temp readout on the ventilation control panel. That is my initial take on what you are experiencing.
Roland