whats wrong

 

Could be a leak in the vacuum line that controls the blend door. I have a pinhole leak in mine...when I hit the AC I have to cycle the thermostat from cold to hot back to cold - when the truck is off, the vacuum line leaks when the truck is off, moving the blend door from cold to the middle. Cycling the thermostat moves the door and fixes it - but only when the engine is running (creating vacuum).

Fix - unfortunately replacing the vacuum line and that's a b!tch to do.

 

fill the freon and waiting for about 3 weeks. if the problem come again, it means there is any leak.