AC blows warm air except in MAX mode, Explorer, Mercury Mountaineer
This one will really make you nuts. You set the A/C on cold and you don’t get any cold air. You’re thinking you’ve got an A/C problem. Low of refrigerant? Bad compressor? But then you switch it to MAX A/C and all of the sudden it blows cold. What gives?
Well, if you’re driving a 1995-98 Ford Explorer or Mercury Mountaineer, the fix may be as simple as a bum blend door in the heater box. This only happens with manual heater controls. So if you’ve got auto temp control, ignore this post. When you turn the temp to cold, the heater control should command the blend door actuator to close off the airflow from the heater core. But these doors are known to have problems. So are the actuators. So if either the actuator or the door don’t work properly, you’re not gonna get ice cold air. It’s gonna be heated air that’s cooled down by the A/C. So why does it work in MAX mode? Because MAX operates a valve that shuts off the coolant flow through the heater core. Take away the heat and you get ice. Get it?
To diagnose this, you have to first remove the glove box the get to the blend door mechanism. Then watch the actuator
as you move the temp dial from hot to cold and back. You should see the actuator moving the door. If it doesn’t, either the actuator is dead or the door is jammed.
Remove the actuator and try moving the door by hand. If it works, you’ve nailed it—bad actuator.
© 2012 Rick Muscoplat
Posted on by Rick Muscoplat