Searched the forum and found several with my same issue of the heat blowing cold when the car is not in motion. Feedback was that coolant was low or had a "bubble" in the system. My coolant level is fine. A poster asked if there was a way to "burp" the bubble out and never got an answer. Anyone have feedback other than draining system?

 

Moved...

 

There is a bleed valve in the line running to the heater core - If I remember it is just in front of the battery compartment. You open that valve while the car is warmed up and running. Might take several attempts. Air typically can only enter the system if you have had a hose off - is that the case? Also, does your temp gauge go up when sitting still? Again, if that is the problem, the gauge will rise, or at least it did in my case. Hope that helps.

 

Do not open the valve all the way, you'll have a huge mess. Trust me. Just open it barely enough so that you can hear the hissing sound of the air escaping.

 

No hoses off since I have had the car(2 years). Problem just started 4-6 weeks ago.

Thanks for the help. Trying the bleed tonight after work.

 

As best I can tell from the 2007 service manual, there's no water flow control valve to the heater core. The discharge air temperature is controlled by the air mix door which is moved by an electric motor.

If burping the system doesn't cure the problem, the air mix door is the place to look. Since it's electrical, I'd look first at the voltmeter to see if the voltage at idle is low.

There's a self diagnostic procedure in the ATC section of the service manual on page 45. There are some places online where you can get a section of the service manual free.