My 2007 convertible has a heat problem up here in cold Ottawa, Canada lately. The heater blows cold air which seems to warm a bit while driving, but turns back to stone cold at idle. On the other hand, I just discovered that if I switch on the A/C on any setting with the temp on warm, it warms up nicely and gets downright hot in the car after a few minutes of warm-up. Coolant level is fine, there are no leaks and airflow inside the car is good. Any ideas on what the problem might be? Thx

 

did you recently have it recharged? or maybe did some recent wiring?

Shot in the dark but maybe you(or someone else) switched some wires by accident since its working the opposite of how it should rather than not at all..

 

My mechanic recently installed a new battery and starter! No new wiring that I know of.

 

Keep in mind the HVAC controls are electronic with microprocessors and switches even though it looks like a "manual" 3 **** system. It sounds like a failure of the switch assembly to pass current to the blend door actuator motor when the heat position is selected. If you are getting heat with the AC on then selecting a hot temperature then this has to be the case. That proves the actual blend door motor is functioning. The blend door motor regulates a flap that directs airflow from either the heater core or the AC evaporator.

This may be as simple as replacing the entire switch control assembly on the dashboard. Check first though to be sure all the plugs are seated properly into the back of the original unit.

You can usually get a good used switch assembly on eBay or from used salved parts.