Thats actually the next thing I wanna try, because I'm all out of ideas...it's a simple system that is kicking my butt...

 

hi there i'm going through the same thing on my f150 5.4. If you search the heater treater fix, in the steps for this it shows you how to get at the heater core and ac condenser from behind the glovebox. I did this in 10 - 15 min with a dremel. You can feel the whole surface of the core and watch the blend door and other doors working as you switch the selector. Just a thought. good luck


Still working towards heat in Oregon, PK

 

Has the heater core been replaced? If it was and the seal that wraps around to core was left out cold air will bypass the core and dilute the incoming air. This will give warm-hot air while setting and cold air while moving due to the increased air flow. Grab the heater core tubes under the hood and try to wiggle them. If they feel loose the seal is missing.

 

Agree no air flow. Check intake side of the coil for blockage, i.e. dirt, leaves, etc. I suspect your system is operative, but you have enought junk on the coil intake side so no air can pass through. That happened to me one time and drove me crazy till I tore everything apart, then it was obvious.

My two cents,

Steve