I think you are "over analyzing" the problem.
If AC is on then you should have 12volts on one of the compressors wires(other is a Ground)
If not then one of the pressure switches has opened so 12volts can't pass.
Power to compressor flows like this:
Climate control fuse(#18)----climate control switch, AC ON(in cab)----AC Cycling pressure switch----AC pressure switch----WOT Relay------AC compressor(clutch)----Ground
WOT(wide open throttle) relay, this cuts power to compressor when driver needs extra power, i.e. gas pedal to the floor, lol, these rarely fail.
If AC temp was warming up at idle then I would suspect low refrigerant level.
You could simply need a recharge.
AC cycling switch opens when pressure in system is too high, compressor pumps up pressure, but it needs to stay below a set level or lines will break, if system gets to hot pressure goes up.
AC pressure switch opens when pressure is too low, not enough refrigerant to compress
Also check the electric fan on the condenser in front of the radiator, it should usually come on when idling, if it isn't working the pressure in AC system gets too high and cycling switch will cut off power to compressor.
While Ford does have compressor clutch "air gap" issues it usually causes other symptoms, and you would have 12 volts at compressor when AC was on, but clutch wouldn't engage, since you don't have 12 volts there it is another issue.
Last edited by RonD; 05-31-2015 at 09:48 AM.