ok guys, i normally have a/c problems figured out but this one has me wondering. im working on a 99 f150. heres the scenario start the truck,drive off and the a/c is ice cold. punch the gas and it goes strait to hot air.(as in the heat is on) i get out with it still blowing hot, check and see that the compressor is spinning and the low side line is ice cold like it should be. (the clutch is engaged) this has me wondering if the blend door isn't somehow switching between the evaporator and the heater core. im guessing its vacuum related due to throttle position when it quits. any ideas guys?

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