I have an 89 big Bronco, 5.8L, 4X4. My A/C works fine when it is at "normal" position. When I move it to "MAX", the air vent changes from the regular vent holes to the defrost after few seconds. How can I fix this?
-fory
You have a vacuum loss problem in the vacuum motor/vacuum hose that controls the outside recirc door. It is located in the engine compartment (Pass side firewall). Possibly the motor is faulty or the vacuum hose is broken/not hooked up/something like that.
When you choose MAX the only thing that happens in the air duct system is that the recirc door is closed to the outside air. Choosing MAX at the function control vacuum switch, vacuum is applied through a small vacuum line to the motor in the engine compartment which then closes the door to outside air. There is a leak in that line to the motor or the motor is bad. (I believe that line is white or has a white stripe on it) The system is going into Defrost because of this loss of vacuum.....Defrost is like the 'default' of the system.....in other words, there is no vacuum or a big loss of vacuum, in the control system. When you chose NORMAL, there is no vacuum applied to that outside recir door.
You should also inspect the check-valve in the vacuum hose system. It is located (near the recir motor) in the vacuum hose from the manifold vac source and the vacuum reservoir. It looks like a 'T'.
Hope this helps.....
Dave S(Texas)
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