Change of seasons sometimes reveals problems with a vehicle that would otherwise go unnoticed. If you have a Jeep Grand Cherokee or a Ford Explorer that has an outside air leak behind the glove box, then you may have a broken fresh air door (AKA Recirculate Door or Max Door). The fresh air door is used to either recirculate air in the passenger compartment or allow fresh air to enter the HVAC (Heating Ventilation & Air Conditioning) system. Surprisingly the Explorer and the Grand Cherokee share a common flaw in the heating and AC system. The fresh air doors are weak plastic that many times under the stress of the control actuator can break. When it's cold outside this problem makes itself very similar. In hotter climates in the summertime, a broken fresh air door drastically reduces the air conditioning's efficiency.
Checking it is easy by operating the fresh air door and listening for increased airflow. When the climate control setting is moved to max, the sound of the air blowing through the vents should be louder because the fresh air door is sealing off the outside air, forcing the inside air to recirculate. If the sound is not louder, you can open the glove box door and look behind it for the operation of the door when switching the setting from normal to max. If the door is not visibly moving, it is likely that it has broken. The door sometimes can even fall to the bottom of the case, positioned right above the blower. It may not be in sight, sometimes you can stick your fingers through the plastic grate and feel the door laying loose on the bottom.
Replacement of the door is not a do it yourself job. The dash needs to be swung out and the HVAC case removed on Grand Cherokees. On Ford Explorers the job can be done without the removal of the case, but the assembly must be replaced. Obviously if the case needs to be removed, the refrigerant must be recovered, which requires an ac machine. So if you are mechanically inclined the one that may be done at home might be the Explorer, of course this depends on your mechanical ability. Even if you are not going to do this job yourself, this information can be used to help explain to the repair shop what the problem is. By providing more information to lead the technician to the problem area, diagnosis time can be reduced.
Source by Dennis Bandy