This AC problem is driving me nuts. I have MAX Air on and the pressures are good, on a hot day, say 95 degrees, the pressures are 38 and 270. The Evaporator line going into the firewall is very cold and sweaty which means the evaporator is cold. the problem is that only HOT air comes out the vents regardless of where the temp control is set. Assuming there is some sort of mixture vane or flap that regulates how much hot and cold air comes into the cab, I guess it might be stuck on the hot side. The vacuum line into the firewall has plenty of vac on it. I removed the control panel and the temp control is working smoothly from about 100 ohms to 5k ohms as it is turned.

What else can I do or check on with this?

 

There is a control known as a GEM module. There a good possibility it is causing your problem. All late model fords have it and it has been quite troublesome.
hanky

 

Another forum pointed me to the blend door actuator. I checked the actuator's 15 amp fuse and it is okay. I started the truck and watched the shaft coming out of the blend door actuator and it does turn as the temp control is rotated.

If the blend door actuator is turning and the temp isn't changing, it almost has to be the door in the plenum is stripped or broken, right? That would also mean a 10-12 hour job to remove the entire dash to get to the plenum, correct?

If that is the case, then there's no way I could do that myself. Any other ideas?

 

The Blend door actuator shaft is broken in the plenum. That's an $850 repair. Instead, we put a shut-off valve in the heater line. Since air always goes through the evaporator, it won't matter if the door is closed and forces it to go through the heater because there is no hot water in the heater.

Close the valve in the summer and open it in the winter. An $850 repair becomes a $7 repair. It's not as slick as it once was, but it does work.