Hey yall, so have a 2001 Ford F150 5.4l. I have looked this thing over and tried everything possible. The heater blows lukewarm air. I have gone through the truck and the blend door and motor work, the heater core is not clogged, coolant is at right level and circulating. I even had a professional look it over and he cant figure it out. I know if i have the fan turned down one notch under high it blows warmer like the fan is cooling the air faster than it takes to get it out of the vents. also when i have the vents switched off of the dash and on the floor or defrost i can feel hot air coming from the dash vent next to the drivers side door and only out of that vent. im wondering is their another blend door or something that i am missing or anyone else have this issue? I figured if it was another door then the guy i had over look it would have caught it but i know everyone can make mistakes and might forget something were not all perfect right. The guy i bought the truck from said that the heater stopped working right after the put in the new A/C system but if i recall that should not have anything to do with the heater at all correct? I appreciate any help

 

you replaced the thermostat?