I am pretty far along in the LQ4 swap into my 89 K2500 and am trying to understand how to wire the A/C up. I really have never retained A/C in any of my vehicles so I am pretty ignorant to how it works electrically.

I am going to be lazy and ask, has anyone swapped on of these trucks 88-94 GMT400s and kept the A/C? If so could you possibly direct me on how I need to wire this up?

I am using the stock harness that’s been thinned out, and my own fuse/relay panel.

Any help or guidance would be greatly appreciated!

 

If truck has original AC use the same compressor power wire to the LS compressor pwr wire and gnd the compressor black wire. Get a LS compressor connector to make it plug and play. FYI - There should be low and high pressure switches that are wired in series of the comp pwr wire circuit to shutdown the compressor if pressures are out of spec. Hope this makes sense.

 

Yes it does actually. My truck did have AC stock, and I had the complete donor truck so I removed and kept everything. I was over thinking this I’d say.
I should be able to leave my stock AC systems wiring as is, and pretty much replace the 89s compressor connector with the 02s connector?

After typing that I realized something, the air inlet pressure switch (closes 220 opens at 170 psi) is located on the original compressor. How will I have that limit switch using the 02s compressor? I plan to use the 89s original al accumulator and make the hoses work between everything else. I am also going to use the 89s condensers too.

Does the PCM just need to see that the AC is on for it to bump up idle speed or turn a fan on? Does only 1 wire go to it?

 

When you buy your new dryer I would get one with a port on it and you can screw in a trinary switch to control the compressor on/off and the fans on/off. If the motor is stock you really don't need any signal telling the ecm to bump the idle. The computer can recognize the load change and adjust accordingly. If you've got a cam in the motor then it may need a signal wire to bump the idle up.

 

That would be perfect. I didn’t know the dryer had a life span and should replaced, but I guess so. I see vintage air makes a switch, I’ll just need to verify the threads are the same and I’ll use that.

thanks for the help!

 

This is an orifice tube system that uses an accumulator on the low side (vs expansion valve system and drier on high side). Low side pressure switch is on accum to turn off compressor pwr when < ~17psi. The R134a retrofit low side switch on accumulator is 15-2832.

I don't see where the factory high pressure switch is. The switch on the compressor shows to turn on cooling fan. You could test and jumper switch connector to confirm. If you wanted, you could add a high pressure switch anywhere in the compressor discharge side before the orifice tube. The switch should open/turn off comp pwr when > 325psi.