I have a 2002 F150 without the EATC. It's been stuck on vent since I bought it last year. I've been driving myself crazy trying to figure it out. Everything I've read about vacuum leaks indicates it will default to defrost with said leak. I can't find anything about one being stuck on vent. Temp control works as does the fan speed. It's ok for now stuck on vent but I don't want to go through another winter without defrost.

 

Check the mode switch for proper operation.

Check the panel/floor vacuum motor.

You don't have a vacuum leak problem, you have a problem where either the vacuum is not being distributed logically (switch) or the motors are not responding correctly. It's also possible that there is a mechanical concern such as a door that is broken, binding, or is obstructed.

 

Thanks for the quick response! I've been afraid all along it's blocked by foam. I don't look forward to removing the dash but I'll probably have to. Can't afford to pay a dealer. Gonna wait til after the 4th.

 

Foam????

 

I have this same problem, no defrost and I'm not quite sure whats causing it. My plan is to go through all the vacuum lines and such before taking the dash apart to see if it's the door causing the issue.
All I do know is I need to get it fixed before winter comes.

 

You need to check the operation of each of the diverter door vacuum motors.

 

I'm not sure what to call it. I'm talking about the stuff they put around the diverter doors to seal them. I've read several posts in different places about it coming loose and jamming said doors. I've even watched a YouTube video where a guy had to remove his whole dash for a couple pieces of the stuff. Thanks to all for the help/advice!