Expert: Mike Evans - 10/10/2009

Question
Just lately, when I turn the heat up to maximum, it results in reduced airflow from the fresh air fan, in any of the fan's three or four speeds. What do you make of this? This is a V6 3.0 with AC.

Answer
    Are you sure it hasn't always done this and you just noticed?  When the system is on Heat, and the A/C is off, the only air coming through the cool side is outside air at ambient temperature.  When you turn the heat to MAX the blending door, which allows a mixture of heated and cooled air into the heater box, completely shuts off the cooled air.    The fan has less air to draw from and is going to produce a reduced volume of flow.  Usually this is not noticeable, though.  I would be suspicious that some foreign material has made its way into the heater box and is blocking flow through the heater core.  The only way to tell, though, would be to disassemble the heater and look.  This is a big job on most cars and a real pain on the Aerostar. If this is really bugging you that's what you'll have to do.