We have a 04 Acura MDX with Navi. This fall the interior temperature, in the heating mode, will continue to climb to very high levels. Not sure how warm it gets in the car but it is very definitely past the setting on the climate control system. The only way to get it to stop heating is to lower the setting to 60 degrees and then cool air comes out of the vents. We have resorted to turning the system off when the car gets comfortable if we remember in time. What part or parts should I be testing for replacement?