I have a 2003 F-150 Supercrew 5.4L. The A/C operates properly for the first hour of a trip. After approx. an hour the air stops blowing out of the panel vents. It does not circulate at all but you can still hear the fan blowing. The only way to get it to function again is to shut the truck off for several minutes.

 

automatic AC or manual? The automatic system uses a number of sensors, any of them that are bad would give the HVAC module false readings, therefore shifting air to other vents, and possibly disabling the AC. The sensors usually read like 3K-15K ohms, high temp=low resitance.

you dont really want to go through and test everything though, if you could get it hooked up to a scan tool you could quickly tell which sensor was bad, also there is a pressure sensor on the AC refrigerant system, too high or low of pressur eand it will disable the compressor.

 

The system on this truck is manual. The compressor still functions but the cold air is tpapped where the air is directed to the vents, defroster or floor. It does not flow from any vent.

 

defrost and floor are the default settings, or like normal settings.... when you turn the ****, vacuum sucks the vent modulator dealy open.... sounds like its going shut when you dont want it to. could be lack of vacuum, could be a bad modulator. if you have a vacuum gun its really easy to test.