Seems Like The HVAC Blows Out The Defrost Under Acceleration

[MattMPA]

I know in many Fords, when this happens...there's a check valve that's not working correctly.

The HVAC works fine otherwise...I can select defrost, floor, etc....

Before I start searching...does anyone know if these vehicle have such a valve...and where it may be?

 

[Tstaats]

I’m knew to PIU life, but, I think I remember reading somewhere that it’s part of the “pursuit mode” programming, usually under WOT. If it’s under (extended) normal acceleration, then it’s probably the vacuum issue you’re thinking of (that I’ve experienced with several of my Ford trucks over the years as well).

 

[MattMPA]

I’m knew to PIU life, but, I think I remember reading somewhere that it’s part of the “pursuit mode” programming, usually under WOT. If it’s under (extended) normal acceleration, then it’s probably the vacuum issue you’re thinking of (that I’ve experienced with several of my Ford trucks over the years as well).

In come cases, the A/C compressor clutch may disengage, but that wouldn't result in warm air or the direction of air changing.

I drove the truck again today....no problems noted. Must've been mistaken, as I can't find any vacuum lines that would feed the HVAC...