I can't figure it out. When I first start my truck, every thing works fine. After I drive for 30 minutes are so the air flow from the vents starts to get less and less. Finally, there is no flow from the vents at all. The blower is still running wide open but no air coming out any where. No defrost, panel, or floor. Shut it off and leave it over night and the next day every thing works fine again and the process starts over. Is there a door that can just completely stop all air flow? Please help.

 

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It does it even with out the AC on. The compressor clutch is not engaged. Should not be due to icing.

 

Go back and check compressor operation, don't assume it isn't operating. It operates in most HVAC modes. See owners manual.

An iced evaporator is the only thing that is logical. If you have a large puddle of water under the truck a few hours after a failure event that would confirm the icing theory.

 

Changed the cycling switch on the low side twice and finally got it straightened out. First one was no good right out of the box.

 

Yep. A cycling switch stuck closed is the most common reason for icing.