I doubt you will be able to keep it sealed pulling the condenser out from in front of radiator, and then reinstalling it
So you are putting the 1999 4.0l w/AC into the 1986 B2, right?
AC is either ON or OFF, so it is just an on/off switch there is no "temp" control.
Temp is controlled by the Blend Door on Rangers and B2s
When you select COLD on the dash slider the Blend door covers the heater core so no air from the fan passes thru it.
If you have AC then the Evaporator will also be in the Air box, so if AC is ON and temp is turned to COLD then you would have full AC cooling, if you slide temp over a bit towards HOT then some air would also go thru heater core and you get a bit warmer air coming out with the mix.
So you really only need an AC ON/OFF switch on the dash that turns on the compressor.
The on/off switch also runs thru the high and low pressure switches on the AC pipes, so if there is a problem you won't burn out the compressor, it would shut off if there was a pressure problem
The 1999 Ranger AC on/off did run thru the Computer, 3 wires
1. AC ON/OFF from dash control, 12volt/0volt
2. Ground from high/low pressure switches
3. Ground for AC on/off relay in engine fuse box
If you turn on the AC(send computer 12v) then computer passes the Ground from high/low switches to the AC Relay, closing it to turn on compressor.
So if a high/low pressure switch was "open" then no AC.
There were two reasons for computer to be involved, if engine temp got too hot computer would turn AC off, when you accelerate and go to WOT(wide open throttle), computer would turn AC off to give driver more power for passing or ??, then turn AC back on when not at Full Throttle.
You can use computer for this or not use it, really up to you