89 K2500 LS swap A/C help

[Tonyorlo]

I am swapping a LQ4 into my 89 K2500. Im using a modified stock harness per LT1swap directions, and my own fuse/relay panel. I swapped an LS into my Porsche 944 last year so I have a good grasp on the swap and the wiring, but I have never messed with A/C. It’s always something I have ripped out and tossed in the garbage. Well for this one I want to keep the A/C. I’ve looked through the factory 89, and the 02 diagrams, but the terminology isn’t the same exactly.

I hate to ask, but could anyone help me out and “hold my hand” on the wiring. From what I understand, the climate control will have 2 wires coming out, one going to the high psi cutout switch, which goes to the PCM. The other will go to the recirc door motor “blend door?” Which has a wire that goes to the PCM also. The PCM grounds the A/C relay. There will be 2 wires coming from the PCM, one to the auto recirc switch, and one to the compressor low psi switch.

I’m sure this isn’t super complicated, I’m just A/C stupid. Any help would be greatly appreciated!

 

[0xDEADBEEF]

I'm in the middle of this on a 96 and I couldn't the pin for the blend door either. (Not sure if it exists.) I believe the one wire that I did locate goes from the dash module through the high and low switches and then to the PCM.

 

[Tonyorlo]

Through searching Google I saw some threads on here with 95 and up information, but I haven’t seen much for the 88-94s. I didn’t read through them so they not of been helpful

 

[Tonyorlo]

Here’s some progress pictures. I rebuilt the NV4500 myself also, something I’ve always wanted to try.

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[Tonyorlo]

Super professional driveway paint job. Good enough for the jambs.

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[0xDEADBEEF]

I was working on my harness last night and was looking over the AC situation. What I have is the one wire I mentioned previously going through the hi and lo switches to the PCM and another wire going from the AC relay in the fuse block to the PCM. I think these are the only 2 wires you really need.

I think the older trucks use a solenoid/valve in the heater hoses to control incoming heat and maybe the later trucks used a blend door. Which means if you want AC and don't have the blend door you'll need some way to block off the hot water coming in. Could be as simple as looping the circuit in summer.

 

[Tonyorlo]

So what exactly does the PCM need to do for the A/C system? Being that my truck had it stock, couldn’t I just use the stock wiring and connect it to the LS compressor? Wouldn’t it work like it did with a SBC? The PCM would normally kick a fan on for it, and possibly compensate for the extra load it would put on the engine?

I didn’t know but it’s suggested to change the dryer if it’s exposed to atmosphere. I am going to get a trinary switch for it, it does both the high and low limits. I’m attaching a pic from the 89 service manual. It shows all AC connections outside of the firewall.

 

[0xDEADBEEF]

So what exactly does the PCM need to do for the A/C system? Being that my truck had it stock, couldn’t I just use the stock wiring and connect it to the LS compressor? Wouldn’t it work like it did with a SBC? The PCM would normally kick a fan on for it, and possibly compensate for the extra load it would put on the engine?

I didn’t know but it’s suggested to change the dryer if it’s exposed to atmosphere. I am going to get a trinary switch for it, it does both the high and low limits. I’m attaching a pic from the 89 service manual. It shows all AC connections outside of the firewall.

I am not really up to speed on this myself, but ...

I think the PCM just needs to see the request and then it will close the relay that engages the AC clutch and also the relay for the efan if programmed. You could technically bypass the PCM completely but you lose the ability to adjust the idle and have it control a fan.

I wouldn't use the LS compressor because it's not in a good location. (I don't think it even fits.) I plan on using the original compressor and AC lines with a mount from LSbrackets.

 

[OutlawDrifter]

You don't NEED the ECU to control the AC on the pickup. You can use the signals to trigger electric fans through the PCM if wanted.

I have the AC running through the original wiring on my 1991 Z28 that uses a 7176 compressor. Just need to make sure you have a high and low switch wired in to control it.

While its apart, I would put in all new components, or at least clean/flush the evap/condensor and hard lines. When converting to R134, run the Ford orange orifice tube, that will help it cool better, lots of info out there about it.

 

[steveed]

The PCM will also disengage the AC clutch if you go over X rpms, mine disengages at 4k rpms.