I have taken our Pontiac in 5 times for different problems pertaining to the heat. The A/C works fantastic. No heat though. Mechanic says it is the thermostat and has replaced it three times, and this last time used a copper, no fail thermostat, which FAILED and now it is currently in the shop again! He says the thermostat is staying open, causing the system to think it is not warming up...I don't know but it is annoying and very cold in the snow belt during the winter. It sucks to keep seeing the check engine light come on a week after the thermostat gets replaced and feel the cold air coming out of the heater. One time I smelled a burning odor and smoke started coming out of the vents! The wires for the fan control knob caught on fire and I had to pull over, shut the car off and pull the fuse for all the heat and air controls to make it quit! We bought the car at 99,900 miles...it is currently at 170,000. I had heat for about a 1000 of those miles.