I've been getting 15-17mpg around town and 21mpg on the open (and flat) road doing 55mph.

Recently while idling my rig after doing work on it I noticed the compressor clutch engaging, then disengaging, and condensation forming on the coolant lines. At the time the temperature control was turned to heat, the selector was set to defrost and the fan was off. I rarely use the air conditioning (I live in the north country) ... is there an easy way to take my compressor off-line? I'd prefer to find a method of keeping it's clutch engaged rather than modifying the compressor to cause it to freewheel, etc.
I've had other cars in the past where turning on the AC would increase fuel consumption by 2-3 mpg.


Portsample
early 1999 F-350, Ext cab, 4x4, 3.73, 105,000, auto, HPX

 

The fan (or system for that matter) isn't completely off unless the Mode switch is in the off position (straight up). Also, in defrost mode the compressor is supposed to run to pull moisture out of the air. The compressor will cycle in every mode except floor heat or vent (or off, obviously). That is by design.

You could just unplug the electrical connector that engages the clutch to keep if off all the time, or wire a switch in series with the same and put it in the cab. You'd have to cut *one* of the wires and connect the wires coming from the switch to either side, if you catch my drift. You could disable it as you see fit from the comfort of the driver's seat.

 

Also, the compressor kicking on once in a while is or was supposed to help keep the compressor in good shape and prevent it from setting unused for long periods of time. Remember the old single contols on older vehicles that you had to bump the AC when you slid from off to heat? I always heard that was the only reason it was laid out that way.