Four problems related to defogger have been reported for the 1997 Mercury Mountaineer. The most recently reported issues are listed below.
Blend air door square drive broken causing severe discomfort in summer and improper defroster operation during adverse weather conditions. Master techs in area indicate problem occures with excess frequency on various model and years of Ford trucks. They further indicate the failure rate is extremely excessive compared to all other makes and models.
While driving, headlights will come off and on by themselves this has happened at night and was very dangerous. Dealer could not duplicate. Customer adds heat blows cold air. Dealer found blend door motor and blend door to be faulty.
Temperature control switch may be defective. No matter what consumer puts temperature on air comes out hot.
The plastic air blend door, which is inside the heater air plenum, broke when the vehicle was just outside of warranty. Two differenet dealers quoted me $700-$800 to make the repair since it involves removing the dash. I cannot bring myself to pay that much money just to have heat in the car, but it is a safety hazard in winter weather since I cannot keep the windshield defrosted.