Adding 94-96 XJ A/C to 87-90 MJ - Slow Thread

[Gojira94]

It's going to take a while to gather everything I'll need to do this. I'm guessing it'll take 6-9 months to gather it all and be ready to do the install. I've chosen to do a hybrid setup, using Renix-era inside parts, aside from the evaporator itself. Under the hood, I'm opting for a 94-96 R134a native setup. I don't like the 97-01 setup that uses stamped metal clips to hold the lines together at the condenser, no thanks. And 87-90 to me looks cluttered and the hoses and parts are hard to come by from what I've seen in discussions here.

 

My engine control harness is from 1989 or 1990 and it has the pins for A/C. My engine harness is from something else and does not have the diode module, A/C clutch relay, clutch feed or pressure switch connectors. I can make all that from parts cut from an 87-90 in the boneyard, or buy the whole harness at the boneyard for about $60 and recondition it.

 

I have the 91-98 compressor mounting bracket, my alternator is sitting on it right now. I'll have to move the alternator down to the original HO location and get a pair of HO alt mounting brackets and shave them for my Durango unit. And a new belt.

 

The remaining parts needed are as follows:

 

HVAC Housing - 87-96 boneyard rehab

Temperature Control Panel for A/C equipped car - 87-96 boneyard rehab

A/C Dash Harness - 87-90 boneyard rehab

A/C Thermostat Control Switch on HVAC box - 87-90 boneyard grab or new Crown 56002688 from Quadratec.com 

Evaporator - new 1994-96

Evaporator drain tube - 87-96 boneyard rehab

Expansion Valve - new 1994-96

Low Pressure Cutoff Switch on drier - new 1994-96 -OR- binary switch Santech MT0484

Receiver drier - new 1994-96

Compressor to condenser hose - new 1994-96

Low Side TxV to compressor hose - new 1994-96

Condenser to drier hose - new 1994-96

Drier to High Side TxV hose - have to have one made after all

Compressor - new 1994-96

Condenser - new 1994-96

Condenser to radiator mounting tabs - 87-96 boneyard rehab + new hardware for them

 

I'm going nuts right now because I have a source vehicle located for some of the big items. But there's no way I can get to it until the weekend of August 8th-9th 2026!

[Gojira94]

First update - the trip to the boneyard was a success.

 

Heater housing bare - $22.50

Temperature control - $36.00

Wiring harness engine - $ 55.50

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Bonus items:

 

Engine control module - $82.00

Shifter bezel - $14.00

 

=======================

$225.20 with 7% tax...

 

 

Computer is a 56006078 - According to an old post by @HOrnbrod, "Renix ECU 56006078 is an alternate (superseded) part number for ECU 53005406."

Mini console has unbroken mounting tabs, so I grabbed it.

 

 

I thought I was smart for going for a 1990/ last year of Renix engine harness. However, this was when Chrysler was starting to dig its fingers into stuff and they unified what would have been 'Engine to Alternator' C105 & C335 on 87-89 88 into this, below (EDIT - 1989 also has these connectors, so C105 and C335 unified into the grey Chrysler connector was either a mid-year 1989 change, or covers all of 1989 MY production):

 

 

They also made a change and unified what would have been C103 (6-way) & C109 (4-way) on 87-88 into this 10-way, below:

 

 

They left C104 alone (10-way). There is also this connector I haven't figured out yet. Where it went was low on the passenger side into a really dirty area I wasn't in the mood to dig into since I was about to tear into the dash. 3-way mystery connector below:

 

 

My verdict is that I'm going to harvest what I need from this harness, rather than trying to use it complete. Yes, I could go get connectors I need from an 87-88 and convert back the changed Chrysler connectors splice them in. I can't be 100% sure C100 is the same as what I have now on a 1988 non-A/C-equipped engine harness (with dealer install connector C117). For me it would be no big deal if I'd had to splice in the fan diode and A/C Clutch Relay and the C100 pins G5, H1, H4 if needed for A/C Request & A/C Select. I've already cleaned up, gone through, and made the modifications for electric fan and fog lights on the harness I already have, and everything else works well the way it is. Better the devil you know than the one you don't. I do already have a (now 100% confirmed) 1989 Engine Control Harness that does have A/C provisions, that came with the project from the beginning, and it's perfect. And it also explains why my trans harness pass-through connector at the ECU connectors from its reverse lights connector is different from the 87-88. And I had to cobble the 2 together to get reverse lights working a while back.

 

Next up is to clean and prep the heater housing. The temptation is to get an evaporator ready in it and when the cool days come back to NC, swap it out with my heater core in it and be done with the cab side of the swap.

 

[Gojira94]

I went back to the boneyard to a 1988 XJ and got the missing pin C / orange wire for C109. I also got the fan diode with radiator temp switch connector attached for my visual reference. And the A/C Clutch Relay socket/ pigtail (which it turns out I won't be using after all).

 

I'd decided against cutting into the 1990 engine harness. I'm going to clean it up a bit, do a few minor repairs around the EGR & ballast resistor connections and offer it up to anyone who might need it/ want it for an 89 or 90 rig. I paid $59.50 for it, so  +$20 and shipping cost and it's yours. PM me if interested.

 

I also ordered a 1996 evaporator and started cleaning up the 1990 HVAC housing. I can see that very slight modification will be needed. The height is over by about 1/4" from perfect. Front to back fitment is good-ish but I'm going to massage the back/ cab-facing lower portion of the box to gain about another 1/4" front-back clearance and settle the rear of the evaporator down about 3/8." It's very close to right and I could probably install it and go with it as-is but my OCD won't let me... pics later.

[Gjeep]

Seems like you're on the right track... Just know you're going to want to keep it to the renix years (87-90) as this is where you started from a pulling parts perspective. 91 was a different set up; '94.5 year-'96 got r134.

 

[Gojira94]

On 8/17/2026 at 3:16 PM, Gjeep said:

91 was a different set up; '94.5 year-'96 got r134.

 

Yessir, and thank you! I am indeed aiming for a 94.5-96 year setup with native R134a. Since I'm fortunate to have the Dealer-Install connector on my Engine Harness, the only hurdles are:

 

1. massaging the 96 evaporator into the Renix HVAC box. The rear bottom corner of the HVAC box (opposite from firewall side) has a radius and needs to be squared a bit for that end to sit low enough. Unmodified it's about 1/4" too high on that end. I used a heat gun and a long socket extension as a finger to make the clearance, so that's done.
2. Make a {relay/ AC clutch turn-on/ low pressure switch/ fan diode} harness for the system. Interesting that dealer installed systems had a harness that looks like it locates the relay somewhere near the dealer harness connector near the factory washer tank, most likely. The compressor coil grounds through the compressor body/ A/C bracket on the engine, so that's the ultimate destination for pin 30 for the relay setup. I already have the diode and its 3 wires. I also already made and installed a factory clone of the fan relay and switch setup during the original build.
3. I will have to run a wire from the diode C245 pin A, making a splice to go to C109 pin C, relay pin 30 and the 96 version of C309 at the compressor.

I made an updated diagram for the dealer installed connector for the 4.0, as I realized the ones in all the manuals are for a 2.5:

 

 

[Gojira94]

On 8/18/2026 at 6:03 PM, Gojira94 said:

massaging the 96 evaporator into the Renix HVAC box. The rear bottom corner of the HVAC box (opposite from firewall side) has a radius and needs to be squared a bit for that end to sit low enough. Unmodified it's about 1/4" too high on that end. I used a heat gun and a long socket extension as a finger to make the clearance, so that's done.

 

This is the spot that needs to be stretched just a bit for a 94-96 evaporator:

 

 

Then the fitment is pretty good. But the evaporator lines may need some room on the firewall side of the box. I trimmed a bit:

 

 

 

[Gjeep]

Looks like the aftermarket is modifying 97+ XJ style evaporators to work with the slightly older setup with threaded nuts. There was no difference in the AC HVAC box HO years r12 to r134. I see though why you need to modify. 

[Gojira94]

Making the harness - first steps. The assumption is that the relay will be mounted on the inner fender well immediately aft of the washer bottle, or strapped to the engine harness with the Dealer Installed A/C connector. Since I've done the 97-01 washer tank conversion, I'm mounting on the inner fender well.

 

5-pin relay is as follows:

85 - to pin B of Dealer Installed A/C connector

86 - to pin C of Dealer Installed A/C connector 

87 - to pin D of Dealer Installed A/C connector

87a - directly to G106, tucked into engine harness loom

30 - join diode pin A behind LH headlamp assembly, extend through engine harness to C109 pin C and compressor clutch connector C309

 

 

To handle the A/C low pressure switch connection, the Dealer Installed A/C connector pin A needs to run to C239 pin 2, at the switch on the receiver-drier. Low pressure switch pin 1 needs to run back to the A/C relay on pin 87. Since I'm running a 1996-copy plumbing setup, my drier will be just below and outboard of the compressor. That means running a wire to, and back from this location, or tying C239 pin 1 into the LT GRN wire just upstream of C103 (upstream = in the direction of C100) for the return path to relay pin 87. The same applies if you're running an earlier setup, the length of wires needed to make the run(s) will be the only difference.

[Gojira94]

Diode, cooling fan and compressor clutch wiring:

 

I did not have the Heavy Duty Cooling option, so I wired in a relay for fan control, copying the factory setup. I'm already using a Renix-era radiator mounted temp switch. To get switched 12V for the relay like factory I tapped into the 14AWG yellow wire  from C100 pin B6, behind the LH headlamp. The yellow wire from the diode/ temp switch connector assembly (C243 Pin B) will go here. I'm replacing the temp switch connector I originally installed with the one in the diode harness I harvested.

 

 

 

Diode pin B to cooling fan relay pin 85:

 

 

The remaining diode pin A will be tied to A/C Clutch Relay pin 30 with a short section of wire along the LH inner fender (since I'm situating the A/C Clutch relay very close to the Dealer Installed A/C connector). At the end shown in the picture below left, I'm splicing a wire over to a second splice near power distribution, along the RH inner fender, joining C109 pin C and a single wire for compressor C309:

 

  

 

So the section of my harness going across the nose of the rig behind the header panel will have 3 wires in it - 1 orange wire to feed a splice on the other side for C109 pin C and compressor C309, plus 2 green wires for the pressure switch connector C239.

 

[Gojira94]

I should go back and explain the source of this connector that will be going into the Dealer Installed A/C connector:

 

 

I took both sides of C109 from one of the roughest 88 XJs I've seen in the boneyard in quite a while. I took a pin out of one side to add the missing pin C on my C109. I used the other side to make this. These colors do NOT match what would have been on the Dealer harness or have any meaning whatsoever. They're just the right AWG in the right places and attached to the right things.

 

The Dealer Installed A/C pins' AWG (engine harness side) for C117 are as follows:

 

D - 16AWG - LT GRN

C - 18AWG - BLU W/TRC

B - 14AWG - ORN/BLK

A - 16AWG - LT GRN W/TRC

 

 

On my homemade connector in the first picture above, I swapped the orange and blue/black pins on B / C, as the blue/black is 18AWG on C109. The orange w/ trace wire on my pin B is 16AWG, not 14AWG per the wiring manuals. That should be no issue, as its job/ current draw is simply to energize a relay on pin 85 (150-200mA). 16AWG has a capacity of 10-13A continuous, short duration up to 15-18A, so a minute fraction of that is fine. 200mA is 1.5% - 2% load vs a wire capacity of 10-13A continuous.

 

Speaking of wire gauge and load, the wire to the compressor will technically only need to be 16AWG as well. The 87-90 Sanden SD-508 draws 2.5A - 4.0A, and the 96 SD-709 draws 3.5A - 4.5A. However, I'll be making the long wire runs for low pressure switch and compressor with 14AWG anyway against voltage drop on runs of more than 7 feet.

[Gojira94]

The receiver-drier part number is the same for years 94-96, 4797002. If you have an HO-era set of engine mount brackets, you'll have this stud to mount it:

 

 

87-93 this may be exactly the same, as the receiver-drier is located in more or less the same place. Heck, the bracket may be the same from 87-01, I just don't have an older one for reference...