Underhood wiring ? for those that have added AC

[bighause]

I'm in the middle of adding AC to my truck that never had it from day one. I have the dash wiring and condensor installed but I'm not sure about the underhood wiring. I have a complete running 89 XJ for my parts donor and there are only 3 wires under the hood for the AC. One orange wire that cycles the compressor clutch and 2 green wires (one with a black stripe) that connect to the low pressure switch.

 

The dash wiring goes thru the firewall and stops at a weatherpak type connector near the air filter on my MJ. Did you just connect these wires to the clutch amd low presure sensor directly or did you have to use the factory relay and other wiring that runs to the relay?

 

FYI both vehicles are 89 4.0's. Thanks for the help, I'm stumped at this point what to do. :dunno:

[HOrnbrod]

Suggest investing in an FSM for your year MJ. It'll pay for itself in six months.

[bighause]

I have the factory electrical manual but it does not go over over how to add AC.

 

Any one with a FSM know if it would help me with this?

[dasbulliwagen]

I don't have experience with the 4.0's, but I guess I got lucky with the 2.5. The FSM showed the 2.5's to have a connector especially for adding dealer installed air. Those wires were allready attached to all the wiring needed in the dash, and I just plugged up my donor airbox wiring to the dash connector for it, and then added the needed relay under the hood to power the compressor, and run the green wires for the pressure switch. The compressor wire is the only wire under the hood that was already existing besides the connector for dealer installed. Somewhere on here is an 88 FSM. That might help you with making the needed wiring for your truck. ait helped with my 87 with donor parts from an 86. Good luck.

[Eagle]

I don't have experience with the 4.0's, but I guess I got lucky with the 2.5. The FSM showed the 2.5's to have a connector especially for adding dealer installed air. Those wires were allready attached to all the wiring needed in the dash, and I just plugged up my donor airbox wiring to the dash connector for it, and then added the needed relay under the hood to power the compressor, and run the green wires for the pressure switch. The compressor wire is the only wire under the hood that was already existing besides the connector for dealer installed. Somewhere on here is an 88 FSM. That might help you with making the needed wiring for your truck. ait helped with my 87 with donor parts from an 86. Good luck.

The dealer-installed air wasn't wired the same as factory air. I have the dealer air in my '87. It's completely different from the OEM air in my '88 XJ and '88 MJ.

 

Since you're taking the a/c from an XJ of the same year, you shouldn't need a diagram -- just move eveything from the donor XJ to the MJ exactly as it was set up in the XJ.

[bighause]

You're right Eagle, the 2 wiring harnesses are very different and I would have to swap over the 2 entire harnesses to do it that way. Using the dealer installed AC cconnector will be much simpler for me, I'm just not sure where to go from that connector.

 

My donor XJ is in really good shape so I plan to sell it once I get my AC working. I really don't want to tear up the wiring on it.

 

Anyone with dealer installed AC want to snap a couple pics of the wiring for me?