I have a 2001 f150 5.4, heat gets warm but not hot and everything pointed to the blend door. Just got done cutting a hole in the dash to get to the duct which I cut into and the blend door is working. I can put my hand on the heater core and with truck idling I can feel it heat up. When i turn on the heat the heater core cools off. Also sounds like ac compressor is cutting on and off. I'm confused on what to look for. Can anyone help?

 

Oleroy there have been probably 5 separate threads in the last 4 weeks that have great info. Use the search button find a wealth of info.

 

I think I've read all I could find, no one says anything about turning the heat on and the ac compressor cutting on and off, it's constantly clicking. If I let truck warm up and turn heat on I have hot air but within 20 to 30 seconds it's cool air.

 

Those blend doors work off of vacuum so since you have an old truck, I would first check that line and replace it if is is damaged (it is the one that goes through the firewall). The A/C is a mystery but it sounds like it might be the control. I would try to disconnect the wire harness from the A/C compressor (it just unplugs) and see what happens.

 

My 01 5.4 does the same thing. (Heats up then blows cooler once I start the blower) I'm flushing my heater core this weekend hopefully (if it gets above freezing). I was told its possibly a partially clogged heater core and not enough hot coolant can pass through the core so it can not sustain heat.

Does yours blow warmer air while on throttle too?

Not sure about the compressor.

 

The ac compressor does not care if you have your truck set to heat. Ac will come on if you have on defrost.

 

Just feel the 2 heater hoses going through the fire wall...if both hoses are the same temp the core is not clogged...they should feel the same as the radiator hoses. If one is hot and the other warm then the core could be clogged...Flush may un clog it...be sure to flush in both directions.

 

I just flushed mine. I went from 90 degrees out the vent before the flush to 142 degrees out the vent after.

Some really nasty stuff came out.

The hardest part was thawing out my garden hose.