Hello everyone.
I'm having a problem with my heat on my 2001 Ford F150 XL 4.2l. I replaced the thermostat, water pump, heater core, blend door, blend door actuator. I even tried adding a heater control valve. The only time I have heat is when vechile is at operating temp, when you first turn the heat on. The longer it is on the cooler the heat gets. Could the control valve be in the wrong way? The valve is installed on the hose coming from the water pump. If I install it in the hose from the thermostat than I don't get heat at all. Could it be a vacuum line?

 

Finally after a number of times trying to figure out what is wrong with my truck, Why I have no heat. It's cause the A/C compressor stays on when it on the heat setting. I changed the water pump, thermostat twice, (first had a 180 in than put back OE 195) flushed heater core, changed coolant, changed blend door actuator, changed blend door. Even installed a heater control valve, which my truck never had since brand new. Removed control valve for now, can always add it back in at a later time if needed. I unplugged the compressor so it stays off and now I have heat.
Now I have all winter to figure out why the A/C compressor stays on when plugged in and temp control on hot and in heat position.