My 2006 Mercury Mountaineer Premier blows cold most of the time. Something will eventually (occasionally) change and heat will come and then stay until next start up. Thermostat is fine, according to temp gauge. Is there any type of reset on the climate control? Guessing it might be a stuck a/c door someplace? How do I access that? Thank you.
With the engine hot, running, and the heater on high, feel both heater core hoses. Both should be hot. If they are, check and repair the blend air door. If only one is hot, try to flush the heater core.