mille_3

iTrader: (3)

Hey guys...been a while since I posted. Tried posting my question over in the cooling section but no luck. Hoping I'll get a response here.

I'm finally getting around to hooking up my A/C but found that the low pressure switch connector on the dryer has one of the wires cut. I'm sure I cut it at some point during my lsx swap but it's been so long I don't recall why.

My question is, what is the light blue wire on that plug? The green one leads to the HVAC control but not sure about the light blue...is it just a ground?

johnw999

I think a green wire runs from the HVAC control to the low pressure switch. Then another green wire runs from the pressure switch to the A/C compressor. The blue wire runs to the fan relay. So when you turn on the A/C, the compressor and the radiator fan both kick on. You can see on the third page of my swap thread that I'm trying to adapt a trinary switch to work with my LS swap and Sanden compressor. I'm still waiting on a part. Once I get that part, I'll have to reroute the green and blue wires.


https://www.thirdgen.org/forums/ltx-...rans-am-3.html

mille_3

iTrader: (3)

Appreciate the reply. My switch only has 2 wires. I'm thinking the blue goes to either fan or compressor but I've got it wired to have pin 17 be the trigger wire and pin 43 to start the compressor (blue/green ECU) but it's not kicking in. I'll have to do some experimenting

johnw999

I reviewed this chart. Maybe the blue wire is the standard color for the HVAC control. I'll try to check the connections on my car soon.

Bullydawg

iTrader: (7)

I am doing the exact same thing! I am running 4th gen controls and the car is Ls1 swapped. Using all the stock AC parts except the 4th gen compressor. I'll be working on mine this weekend. I'll let you know what I figure out. I'm pretty sure the 4th gen controls have 1 less wire, and I believe the control just needs to run to the PCM and it will control the compressor...

mille_3

iTrader: (3)

That's my thought too, but the green wire from the HVAC control is not triggering Pin 17 unfortunately.

Bullydawg

iTrader: (7)

Figure it out? I hope to be wiring mine tomorrow...

mille_3

iTrader: (3)

I'm thinking my blue/green ECM is not triggering on pin 17. I'm told that the pin can be used to trigger the compressor relay but it's not working.

Instead I'm just bypassing the ECM. Wired the green wire from the HVAC controller to the fan relay so the fan turns on when I wnat A/C and then the low pressure switch wire (blue) that was cut directly to the A/C relay trigger wire. From all the wiring diagrams I've found the blue wire seems to trigger the compressor anyway. So far so good.

johnw999

I think you're on the right track. I looked at the wiring from my low pressure switch. The blue wire goes to the A/C compressor.

Bullydawg

iTrader: (7)

Did you happen to get it working? I've ran into every snag possible reinstalling the AC components, should finish today and hope to wire it next weekend.

QwkTrip

iTrader: (22)

The AC wiring changes color so much that it can be confusing if you don't have a wiring schematic for your vehicle.

To answer you first question, the LT BLU wire leaving the low pressure switch goes to the high pressure switch. (It probably changes color by the time it gets to the high pressure switch.) The original set up of your car is that the low and high pressure switch are wired in series between the LT GRN wire of the HVAC head unit and the compressor clutch. The wire color changes each time a wire enters or leaves an electrical connector. There could be a relay somewhere between the high pressure switch and the compressor clutch, depending on the vintage of your car. If there is a relay, then all you need to do is let the engine ECM control that relay.

Also, the engine ECM needs some way to know that AC is being requested. I don't use an LS1 ECM so I'm not sure what it is looking for, but you need to give it the kind of signal it wants to see in order for the ECM to know that AC is being requested.

I would suppose (but don't know) that the LS1 ECM is simply looking for a +12V signal that the AC system is ready to operate. If so, then the logical place to grab that is between the high pressure switch and the compressor relay. If your car originally had a compressor relay then it is likely the case that the wire is already there and you just need to repurpose it. There is a DK GRN/WHT wire that runs between high pressure switch and the compressor relay. That wire probably splits into 2 legs somewhere (likely at the relay connector), with one leg going to the compressor relay, and the other leg being the +12V signal for the engine ECM.

So by now you have read through my long-winded post only to find out I don't know the answer. But I've been waiting for somebody to post that does and it hasn't happened yet. Tired of waiting so I thought I would try to help.... don't know if I did or didn't.

Chuck!

If you're using a blue/green PCM then most likely the stock output is serial when the relay is looking for a ground. So you'll need a tune if you want to control it via pcm.

https://www.thirdgen.org/forums/ltx-...reen-blue.html

Thanks
Chuck

mille_3

iTrader: (3)

I got it working and bypassed the ECM. Wired through a relay similar to how the car was originally wired. Got tired of trying to figure out why ECM wouldn't control it.