No Power at the A/C Compressor, clutch isn't engaging????

[Twilightcall]

I replaced my a/c compressor the other day. I ran a good vacuum on it and it held for an hour and a half. Charged it up and it was ice cold. Worked great. A few days later I drive the car and no a/c.
I check and the clutch isn't engaged. I checked for Voltage at the compressor. No 12V. I check the amount of Freon in the system. It is full. I then ran seperate wires to the compressor from the battery and the clutch engaged. So my compressor/clutch is functioning fine but still no 12V. I checked all of my fuses and every one checked out.
What could it be? I was thinking in one of the pressure switches???? I am not sure how to test them. Any ideas on what to test would be appreciated with how to test them. Thanks.

 

[Glacier991]

When you have seleced a mode where the AC runs (AC or defrost for example) power is routed from tyhe AC switch on the dash through the low pressure cutout switch, located on the accumulator. If the lp cutout senses pressure over a certain amount it will be a "closed" switch, and the current then passes to a Wide Open Throttle module (desgned to cut off the AC in conditions of wide open throttle). If the throttle is not "wide open" this in turn should be "closed", and the 12V should pass to the compressor clutch. I'd start by jumping the connector hooked to the low pressure cutout. (make sure you have selected AC mode in the car). If the AC now runs, replace the switch (FORD calls it an A/C cyclic switch I believe). If it does not, suspect the AC switch in the car, or the WOT module. Odds are it is the low pressure switch. Oh and, by the way, you can just screw it off, it is on a schrader valve. I think there is a plastic one out now, and if you use it as a replacement, tighten it only finger tight. Use mineral oil on the O-ring if you replace the switch.

 

[Twilightcall]

Thanks for the info. I will try that out. Does the harness just pull right off of the switch.

 

[Glacier991]

yes, straight off.