1988 mercury grand marquis A/C compressor not working

hi everyone. My 88 merc a/c compressor doesn't turn on when selected. I can hear the solenoid open to allow refrigerent to cycle. I hooked the compressor directly to the battery and the clutch engages and it sends cold air right away so it is fully charged. it is something electrical either a relay or switch that tells the compressor to start i would assume. My repair manual sucks for an electrical break down so if someone has a good diagram plus an idea of what the problem is it would be much appreciated, as well as where to locate the the possible switches in the car itself. Thanks

Since the clutch pulls in and blows cold as soon as you feed it battery voltage, the compressor and the charge are fine, and the fault is in the switch side of the clutch circuit.

On these cars the clutch feed passes through the clutch cycling pressure switch, which sits on the accumulator (the can on the low side, near the firewall). Unplug it and jumper across the two terminals in the harness connector with the engine running and A/C selected. If the clutch engages, the switch is the problem (or the charge is low enough that the switch is doing its job, so confirm with gauges before replacing it).

If jumping the switch does nothing, put a test light on the clutch connector at the compressor with A/C on. No power there means the break is upstream: the A/C control switch, the fuse, or the relay the engine computer uses to cut the A/C at wide open throttle, which is normally closed and rarely the cause.

If your car has the automatic temperature control, we have a 1987 Crown Victoria and Grand Marquis ATC wiring diagram that shows the A/C clutch circuit with wire colors. Cars with the manual control are wired differently:
https://www.supermotors.net/reference/ford/ltd-crown-victoria/1983-1991/wiring-diagrams

Dana