Yea, the A/C control systems between the Ranger and the Expo are completely different.
In the Ranger, the A/C clutch relay is always powered and the PCM has 100% control of when the A/C runs. The switch on the dash simply goes to the PCM, not to the a/c components.
In the Expo, the PCM is simply a switch in series with the rest of the a/c controls to turn off the relay under WOT.
So, try this:
Remove the A/C clutch fuse
On the Ranger side of the 42 pin body harness/engine harness connector, loop pin 35 to 37 and neither connected to the Expo side of the 42 pin connector.
At the high pressure switch, cut the black/white wire and route the pressure switch side of that black/white wire to both pin 37 on the Expo side of the 42 pin connector and the "cold" side of where you removed the fuse for the a/c clutch relay. That "cold" side goes straight to the relay's pin #1.
That black/white wire was the path to ground after the high pressure switch so once cut from the switch, can't do any harm.
Pull the A/C clutch relay and using male/female push on connectors and a bit of wire to make some extensions, connect pins 1,2 and 3 on the relay directly back to the sockets those pins originate from but connect pin 4 on the relay to the socket for pin 5.
Once done, the relay will only get powered when the dash switch is set for A/C and the pressure switches and PCM allow the compressor to run.
In short, looping pin 35 to 37 directs the power from the dash switch into the pressure switch circuit and routing the black/white wire to the relay will energize the a/c clutch coil with that power.
Routing that power back to the PCM "tells" the PCM you've called for A/C so it knows to control the clutch relay under WOT.
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