1996 K1500 A/C Wiring Explained for LS Swap.

1996 Chevy K1500 GMT400 AC wiring explained.
I say 12v repeatedly, please note that I am referring to ground, the AC signal grounds the computer (I think) and then the computer grounds the relay. The only 12v output on the diagram is the clutch wire leaving the fuse block, everything else is just supplying or interrupting ground.

[@scottcoleman284]

Great job, the only thing I would add is that the LS pcm does need an ac signal to know when the compressor is engaged, so that it can adjust the idle accordingly for the additional load on the engine.

[@azhandyandy]

Loved your no-nonsense info. Refreshing and informative

[@aaronwilliams6562]

Thank you good information I am fighting this problem right now on my LS swap obs crew cab

[@spencerwelch5422]

My goodness, I'm flat stumped. I've had my swap done for two years now. Had a baby girl and halted everything. Daughter loves to ride in the truck, but it's too hot. I'm trying to utilize the factory fuse block etc. My "low pressure" sensor has the dark green wire cut. My "high pressure" sensor has the green/white wire cut. I think I've found the green/white wire that was cut and reconnected it. I've cut the group of orange wires coming from the back of the 10 amp fuse. Need to trace where it goes. This truck does nothing but set since I've finished it. It's too hot. Wish you were closer. 😞

[@deej2985]

Also I have the 95 r4 compressor which was a 134a

[@deej2985]

Any advise would really help me

[@seanclement2264]

What harness did you get those two wires from is it from the pcm or from somewhere else?

[@TheOGBigShow]

I’m going to run my ac off of my obs harness. I’ll connect the two wire to get around the computer. Will I need anything else 5v/ground etc to make it work? Or when it goes back to the fuse block it get power and ground from there? Mine is a 98 2 door tahoe. At the end you said the 98 was different? How so?

[@matthewevans8469]

I dont know how the 98 ac works, i know the 96 and 97 are the same truck. The 98 had some subtle changes, like the fuel gauge runs through the ecm. The high and low cut outs just interrupt the clutch relay ground, either through the computer or can be wired directly, no extra wire needed.

[@charlesevans7152]

Where did you find the C 100 pin out? I have a 97 sierra and the 96 pinouts are the same.

[@arolon9173]

Did you get the C100 Pin out for the '97?

[@michaeledge2375]

Working on the exact setup here. 96 LS swap. I'm losing ground between the control unit and low pressure switch. Where would you start to trace?

[@matthewevans8469]

I would remove the backing plate on the c100 by lifting the tab against the wires and sliding the backing plate away from the wires. Once the wires are exposed find the light green wire identified in the video and put a diagnostic pin through the wire, see if the signal is present at that point (I believe it is ground but cannot confirm this, it might be 12v). If there is no signal coming through then the problem is inside the cab, I cant help you with that one. If the signal is getting to the c100 then confirm it is the one wire by putting the diagnostic pin on the light green wire near the low side cycling switch and directly send the signal and see if the ac cycles appropriately, then you have confirmed the wire is at fault and can replace the wire.

[@matthewevans8469]

Remember that the ac must have some charge for the clutch to engage at all, a vacuum system will be stopped by the low side.

[@Chicothadonn]

Working on a 96, but im running the r4 style compressor, with no canister, is it possible to bypass that wire on the canister to only use the wire for the dryer ?

[@matthewevans8469]

That will work, i believe thats high pressure, so having that cut off the ac if pressure gets to high is sufficient for safety, for efficiency you want a low pressure cut off, but its optional.

[@Chicothadonn]

@@matthewevans8469 thank you ima try it out, another thing i originally have 4x4 but i am not running the transercase that harness on top of the c100 is it needed ? or can i jus not have it plugged in ?

[@deej2985]

I need some help myself same everything u have year and all I don’t know where to put them green wires at in the 99 ls 5.3 pcm red and blue connections plz help

[@matthewevans8469]

There are pinouts for those on lt1swap.com

[@deej2985]

I have tried them no help really I’m pretty sure I have it right everyone is saying ground pin 55 I have no pin there I took it off because lt1swap said too it won’t come on and the funny thing is that his is the second compressor brand new not reman and acts funny when I jump it it get so hot in the matter of less then 5 seconds I can’t touch it I hate when I put 12v to it to activate the he clutch and also the orfice tube got suck d in past the stoping point ac worked before the swap now it don’t I’m so lost

[@deej2985]

Do u remember what pin locations u put yours and does it work plz and thank u