A failed heater blend door or actuator can cause the temperature control for the HVAC system to stop working. A clicking sound from the dash area would commonly indicate an actuator fault. If the heater gets stuck on the hottest setting, the heater blend door may be broken requiring replacement of the heater box to repair the issue.
Problems for specific Mercury Mountaineer years:
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Most reported 1999 Mercury Mountaineer problems
The composite (plastic) intake manifold may crack near the thermostat housing and cause a coolant leak. Ford released an updated manifold that was reinforced to prevent a recurrence. No recall was issued for this problem but Ford did extend the warranty to seven years on some models from the date of purchase.
The rear wiper may stop working. This could be due to a rear wiper motor that has failed requiring replacement.
The rear window wiper may not fully contact the rear window. To fix, replacement of both the wiper blade and wiper arm is necessary.
The intake manifold O-ring gaskets commonly leak, causing stalling and poor idle quality; the Check Engine Light will illuminate.
4wd vehicles may develop a squealing noise coming from the front wheels when driving below 30 mph. This is generally caused by dry excluder seals, lubricating the seals will commonly correct this concern.