Just got back from a long trip towing our travel trailer, our AC was not working properly, it would get to a point where there was not nearly as much air coming through the vents. When I stopped for fuel I looked around under the passenger side and noticed some moisture drops under there. I turned off the AC and ran just the vent fan and airflow gradually returned. It would seem as though it is frezzing up. Truck is an 05 5.4. I had checked refrigerant before I left as it didn't seem as cold as before and that was full.

 

How was the refrigerant level checked? Low refrigerant level is the usual cause of the evaporator freezing. It could also be due to a partially blocked capillary tube.

 

Usually, a stuck low pressure cycling switch is what causes evaporator icing.

 

I agree. If the low pressure cycling switch was working correctly, this should prevent evaporator icing with low refrigerant.

 

No, low refrigerant level will cause the cycling switch short-cycle, not remain closed. For whatever reason, the clutch is remaining activated even when the evaporator temperature (as determined by the low pressure cycling switch) drops too low and should cause the clutch to disengage.

BTW, no capillary tube on Ford CCOT systems. Normal compressor cycling is controlled by the cycling switch.

 

I'm calling an orifice tube a capillary tube.

 

A restricted FOT should cause short-cycling also, but with fast-rate suction-side pressure swings and a low to normal discharge pressure. The clutch will usually remain engaged for short intervals and remain disengaged for longer than normal periods.

Does this 05 have a cabin filter? If so, it may be dirty enough to cause reduced airflow through the evaporator such that, when driven in humid weather, contributes to freezing conditions.

 

I couldn't find a cabin filter because that was my first thought. I looked under the glove box. I also looke in the manual and couldn't find any info on it there either.