We have a 97 f150, 4.6l auto.

When we turn on the heater, it works for about 60 seconds and then turns into cool air! If we turn it off and wait a few minutes, we can turn it back on and it will repeat, with warm air, then turning into cool air!

I do notice the a.c compressor cycling when you turn the heater on. I do not know if that's normal for this truck. I'm thinking it could be the heater core not flowing enough water, but its not likely, but thats what it reminds me of.

We had this problems since we bought the truck earlier this year, I did have a recent engine and radiator flush(to make sure it had proper antifreeze) and the techs couldnt figure it out, but suggested it was the thermostat, even though the gauge doesn't fluctuate and holds steady in the middle of the gauge.

 

The compressor should not cycle with the **** in the FLOOR or PANEL positions.

 

The a/c cycles on the panel position. The only position it does not cycle on is the floor position. What would cause that?

 

In any event, it's not relevant to the symptom.

See your other thread to continue this discussion.

Try to keep everything related in a single thread. You've got at least four different threads open on this problem.