I have a 2001 f150 super crew 4x4 with a 5.4L that had a vaccum leak that made the ac default to defrost all the time. I have found a vaccum leak and repaired it, and the problem was not as bad. the ac defaults to the defrost now only when the motor is under a load, I have looked for more leaks but have not found any more. Does anyone have any suggestions or hints to help me out, could there be any type of vaccum valves that may not be working or could be a problem somewhere else any help would be great.

 

There should be a one way check valve in the inlet vacuum line. This valve keeps vacuum trapped in the control head so the air blows out of the proper selected spots.

 

did you ever figure out the problem? I'm having the same problem and haven't been able to find any leaking vacuum lines. What's odd is it only switches to defrost when the a/c is set to max cooling , move it back to reg. a/c and it doesn't switch, I know I'm missing something. Anyone help?
Bruce

 

I am having the same problem have checked the vacuum lines and the check valve, all are good. Have noticed that it only defaults to defrost position when the A/C is operating in max a/c. I have the EAC digital control. Could this be a bad relay for the blower door and if so where is it located? Also, what does the sensor in the top of the dash control? Thanks