I'm a new 09 Avenger owner. Here's the background,
Just had the thermostat housing changed, Coolant is full, no trapped air. 100% certain.

Heat goes from hot to cold at random and changes when it wants. I can't change whether it's defrost or floor.
I've read there are ways to test/reset the blend doors etc. can someone give me a clue or two? Thanks!

 

Check your heater control valve, turn the heat up to high and feel the hoses connected to the valve. If only one side is hot, then you need to replace the heater control valve.

 

Yep, both are hot. It seems to be the HVAC control. I'll get a blast of cold air, then it will switch to all cold. When that happens I can't change from defrost to floor or vent. It's stuck where it is. Some times it only lasts a few minutes but yesterday it was that way for 45 miles. My wife was NOT happy. I stopped at AZ to get codes but their scanner doesn't do those.

 

sounds like the control...but could possibly be a door or actuator problem...the problem with these newer cars is that more and more are using "can" communication where instead of having voltages and grounds you get communication between the different modules in the car on data lines by means of pulses so it will most likely be a dealership job to diagnose...

 

Talked to the stealership today and a scan is $85. She ruled out the blend door actuator as it's not cold on one side it's both. Soooo I think I'll put the $85 toward a heater control.

 

Popped for a new heater control. All is well now. I've seen some core charges on other sites. Anybody know of a place that buys them?