I have a 1997 Ford F-150 with the 4.6L V8 engine. Heat has been an issue since I got the truck last fall. There is some heat in the cab, but very little. It is enough to defrost the windshield, but that's about it. The AC works great.
What I have done;
- Changed the thermostat (replaces with OEM specs)
- Flushed the cooling system (air removed, both heater hoses get hot)
- Checked the blend door (big pain to get to, but it is not broken like a lot of posts I found)
- Checked the blend door actuator (working well, not stripped)
- Checked heater controls - Fan, temp and selector all work
While I was in the heater box, I ran the engine. The core is heating up, but there was no air flowing thru it. It felt like all the air was coming thru the AC evaporator side. I had limited view inside the box because I cut a 4" x 4" hole in the box behind the glove box to access the blend door without taking the dash out.
I have not been able to find a diagram of this heater box / system to see how the airflow works with this system.
What is keeping air from passing thru the heater core?