Cross posting my post from another thread:
Just to throw this out there pertaining to the A/C. Im doing my second KL swap into a P5 and making things as close to factory as possible, including the A/C. After a bunch of head scratching I figured out the best approach.
Note that this is using an OBDII Probe harness. OBDI may be slightly different.
First, you use the stock FS compressor by making a adaptor plate to mount the FS compressor to the KL block. Ive been using 3/8" thick aluminum plate with spacers. Remove the FS clutch from the compressor and replace it with the KL clutch. It swaps right on. Boom, no mixing and matching lines.
Next, run the A/C amplifier output wire to the A/C high pressure input on the KL ECU. This was labeled as the "A/C on" wire on the FS ECU. This will tell the ECU that the A/C button is pushed, activate the fans, and bump the idle speed to compensate for the extra load of the compressor.
Last, wire the A/C relay output on the KL ECU to a fused relay to feed power to the compressor. The output from the ECU is a ground.
Somewhat simplified explanation on how it works: The KL a/c system uses high pressure and low pressure switches in the system to cycle the compressor. The low pressure switch prevents compressor damage from too low levels of refrigerant. The high pressure switch shuts down the compressor when pressure is too great, which would eventually freeze the evaporator core. In the P5 system, its simpler. It still uses the low pressure sensor for the same function, however it is used in conjunction with an A/C amplifier. The amplifier uses a temperature probe to monitor how cold the evaporator is getting, and will cut off the compressor to keep it from freezing up, then cut the compressor back on once the evaporator is above freezing. The output of the amplifier goes through the low pressure switch, so its essentially two sensors in one. The output of this goes to the KL ecu through the high pressure input to tell it to turn on the fans, compressor, and bump up the idle. The KL ecu will also shut off the compressor under wide open throttle.