I have a 98 f150 with a 5.4 in it ,and when i turn on the heater i hear a click and the rpms rise a little i looked at the ac as the truck is running and see it turns on and then off. i turn on the ac and it works great and also the heater,and when i turn the **** to off it goes away, rpms stay even.think the problem would be in the heater ac switch thanks

 

Welcome to FTE bearrug! What you describe is normal operation. The only two operating modes that the AC compressor is not used is in the OFF and VENT positions. All others it is used to pull humidity out of the air to keep fogging down.

 

thanks for the info i just remember it doing that before i thought it may have been a leak or something

 

I beg to differ.

IMO the only three operating modes that the AC compressor is not used is in the OFF, FLOOR, or PANEL positions. The AC is also designed to cut out below a specified temp ~50 degrees. AC & heat can be blended together in the other positions for the widest range of temp, humidity & defogging combinations. FLOOR or PANEL should be used for maximum heat w/o AC running.

Not sure what "turn on the heater" meant? IMO the TEMP control turns on the heat & by itself you shouldn't "hear a click and the rpms rise". The blower runs in all positions except OFF & coolant circulates whenever running, so that heat is quickly available when damper opens.

 

Club Wagon is likely right on the modes. I was recalling from memory and it seems to be failing me more often these days.