ECU Air Conditioning

[Elwiscon]

Help! I’m in the process of retrofitting AC on my 89’ 4.0 non-AC comanche, so far I have:

 

-Replaced the dash heater/ac control, HVAC box and HVAC harness from ac-specific from a donor XJ

-Installed a new evaporator, lines, compressor, condenser, expansion valve etc, still needs to be charged.

-Installed new thermistor temperature sensor in the evaporator.

 

I traced the wires from the spare 4-wire connector on the driver side, one of the green (or green/black) wire is the “input” from the dash control when the dial is in the AC positions, the other green (or green/black) goes to the thermistor, which closes and sends power to ECU via the tan/white wire. On the same 4-wire connector there’s also an orange/black which is the fuel pump circuit, then the blue/white goes to the ECU as “ac select”. I plan to use an aftermarket 30A relay to start the AC compressor.

On the AC, I’m assuming the tan/white input to the ECU is the signal so the ECU idles the engine at a higher RPM when the AC is on, the green is the signal wire going to the AC pressure switch which provides power to close the AC compressor relay and turn it on. Does anyone know what is the blue/white for? On this Haynes diagram it goes to the AC relay coil (see picture), and the orange/black from the fuel pump seems to be part of the coil. How critical is the blue/white wire for AC? The way I see it the green and tan/white are important to initiate the AC. I can figure out and wire the compressor with an aftermarket relay, the green from the ECU goes to the AC pressure switch and the load side of the pressure switch will kick on the relay for the AC compressor and auxiliary electric fan (both wit diodes). 

How critical is the orange/black (fuel pump) and blue/white (AC select) 

By the way, I left the original wiring under the hood, didn’t want to replace it with an AC-specific engine-bay harness, it should be very straight forward once I address the ECU wires.

 

Any help will be appreciated Thank you all! 

 

[Ωhm]

9 hours ago, Elwiscon said:

How critical is the orange/black (fuel pump) and blue/white (AC select)

 

ORG/BLK fuel pump wiring is an ENGINE RUNNING ONLY voltage, not KEY ON voltage. BLU W/TR is used for grounding the AC Clutch Relay via the ECU and not AC select (LT GRN).

[Elwiscon]

1 hour ago, Ωhm said:

 

ORG/BLK fuel pump wiring is an ENGINE RUNNING ONLY voltage, not KEY ON voltage. BLU W/TR is used for grounding the AC Clutch Relay via the ECU and not AC select (LT GRN).

Makes sense! So i will use the orange/black to trigger a separate relay so the AC compressor clutch engages only with the engine running, then use the blue/white as a ground. I think I will have add another relay to switch constant power from a dedicated circuit fuse, with blue/white and orange/black as triggers (coil) then the load wire on that relay will be the line on the AC compressor relay which will be triggered by the chassis ground and load side of AC pressure switch, that way the ECU still grounds one relay, i’ll do some testing, i think we got it figured out. Thank you 

[Ωhm]

The ECU will only pick the AC Clutch Relay (BLU W/TR) when both AC Request and AC Select has voltage on the ECU pins (C201_C2 & C201_D2). Maybe I'm missing something here.

[Elwiscon]

11 hours ago, Ωhm said:

The ECU will only pick the AC Clutch Relay (BLU W/TR) when both AC Request and AC Select has voltage on the ECU pins (C201_C2 & C201_D2). Maybe I'm missing something here.

Got it, I’ll have to do some testing before making the connections and assembling the system, so the blue/white (ground) only sends a ground when the green and tan wires at the ecu get power? LIke i mentioned I’ll be using a new fused circuit and relays to start the AC clutch, just want to make sure i do the control part correctly, especially with the ECU being part of it. Thank you