WHILE WE WERE DRIVING THE VEHICLE, THE BLOWER MOTOR FOR THE AIR CONDITIONER SHUT ITSELF OFF THEN CAME BACK ON AND IT WAS BLOWING WHITE SMOKE OUT OF ALL OF THE VENTS. WE HAD TO PULL OVER TO THE SHOULDER OF THE ROAD AND SHUT OFF THE CAR IN ORDER TO STOP THE WHITE SMOKE FROM COMING THROUGH THE VENTS. THE HVAC BLOWER CONTROL MOTOR UNIT HAD STARTED BURNING AND FAILED TO DISENGAGE THE BLOWER MOTOR WHILE IT WAS BURNING. ADDITIONALLY THE VEHICLES 40A FUSE AND 30A ISO RELAY DID NOT WORK PROPERLY, IF WE DID NOT SHUT OFF THE CAR IT WOULD HAVE CONTINUED TO BURN. THIS IS THE SECOND INSTANCE OF THIS HAPPENING TO OUR MERCURY, THE FIRST TIME WE WERE PARKED AND WHEN WE TURNED THE CAR ON IT STARTING BLOWING WHITE SMOKE AND SMELLED OF BURNT ELECTRONICS AND OZONE FROM AN ELECTRICAL FIRE IN THE CAB. WHEN WE HAD A FORD SERVICE CENTER LOOK AT THE VEHICLE, WE WERE TOLD THIS IS A COMMON PROBLEM WITH THIS TYPE OF VEHICLE. AND THAT THE CONTROL UNIT IS BEING USED LIKE A FUSE TO THE BLOWER MOTOR. *TR