adding A/C to a 91

[Pete M]

how much of the wire harness is different?  my searching keeps flooding the page with recharges and 134 swaps and I can't find a conversion swap specific to the early HO Jeeps

[ghetdjc320]

I don’t think I’ve ever seen an HO XJ/MJ without ac. That being said, the engineers who designed these harnesses had a propensity towards over complication of wire routing. The actual circuit connections are quite simple. 
 

Once you have the ac hvac control deck and wiring connector, splicing in what you need shouldn’t be a problem. Basically you get an AC select signal (don’t recall if it’s ground or 12v + but it comes from the ac control deck) that goes to the ecu. The ecu then sends out an ac request signal that goes through the AC pressure sensor. The ecu then has a compressor trigger output that will go to the ground terminal of a 20a relay to kick in the compressor. Ultimately, you could bypass some of the computer controls of the AC but you will loose some features such as idle kick, and provisions to turn off the compressor with different engine parameters such as wide open throttle and engine overheating conditions or whatever logic the ecu is programmed with for ac control. 

[Pete M]

it's one of those weird super base model trucks but with the 4.0/4x4 added on.   originally a radio delete too. 

[Gojira94]

Did they provide a 'dealer install' connector in 91? If so, that's not super hard. There is a distinct difference in the heater-only A/C dash harness and the one for A/C-equipped. If you get the box, control panel and harness you're most of the way there. PM'd you a couple of wiring diagram images for 91 MJ.

[Gojira94]

3 hours ago, Gojira94 said:

Did they provide a 'dealer install' connector in 91?

 

Appears not. Following up @ghetdjc320's comments you'll likely have to scab onto the A/C connectors dash harness connector(s) and pass them through a firewall grommet to create the connections to AC Request --> AC Clutch Relay, and Low Pressure Switch. The AC Select stays inside and goes to the Thermo Switch at the evaporator. Working on getting you some decent resolution diagram screens from Mitchell.

 

I suppose it's possible the equivalent of bulkhead connector C100 has the wires in it from the heater harness connector for some of the AC functions, but I'm skeptical. Once you get into the dash you'll know more from looking at those dash harness to heater control connectors.