[beking32]

Wiring

This can vary depending on your setup and what kind of harness you use, and if you decide to use some of the stock wiring, fuses, and relays. Lt1swap.com is your friend. Almost everything you need to know, regarding pin outs and wiring, is on that site. You honestly don’t need much from the stock PCM. I kept my A/C and got all the wiring info on that from the post on here from that one guy Jose. Also kept my ABS, and luckily all the wiring for that is separate from the PCM. I cut out all the wires I didn’t need from the stock connectors and separated what I did. Then I opened up the whole stock harness and pulled out all the unused wires. Wrapped up everything in cloth tape. Made a new harness for the fuel pump, since the new harness had its own fuel pump relay. I used the stock fan relays and wiring by using the signal wire off the stock PCM. I went with a new harness for the engine to keep it simple. Didn’t want to drill into firewall so I put the LS PCM in the stock location and fuse box not too far away from it. Could’ve done a better job at hiding all the wires, but I was in a rush to get it running. And to keep it simple for all you b body guys, this is what I used from the stock PCM. Keep in mind this is for a 95 so I don’t have a tach signal to save off the PCM:


Red connector

Pin 10 - sec fan DK BLU
Pin 11 - prim fan DK GRN
(Ground signals for relay)


Black connector

Pin 1 - A/C request signal DK BLU
Pin 8 - VSS speed
Pin 21 - A/C clutch status DK GRN



Clear/Gray connector

Pin 14 - brake switch PPL
Pin 15 - park neutral signal org/black (optional)



Blue connector

Pin 3 - PCM ign feed PNK
Pin 8 - A/C clutch control DK GRN/WHITE
Pin 9 - Check engine light
Pin 12 - A/C refrigerant pressure sensor RED/BLACK

What pcm are u using?

 

[beking32]

A/C

So like I mentioned before, I got my info on the A/C wiring from the post mentioned above. Everything works like it should but there are a few things that are not mentioned in Jose’s post. If you are using a truck motor with a truck tuned PCM, it gets a little tricky. This is for an 0411 PCM with DBC. In order to get the PCM to read and power the correct pins for the A/C, you have to use a 98-2001 truck or car tune. The pin outs are on lt1swap.com but under the car section, not the vortec/truck section. Reason for this is that these year models came with manual A/C with a pressure switch, just like our cars. The problem I kept encountering though, no matter what year, or truck, or car, is that the fans are always on no matter what. It’s a problem with 2001 and under tunes not being able to run electric fans correctly since the vortec motors did not come with them. In order to fix this, you have to use a 2002 tune with an OS of 12212156 for electric fans to run correctly. Problem with that OS and tune is that you lose A/C because GM switched over to using a low pressure switch and HVAC module to control A/C. I have yet to find a tune that can run fans at the proper turn on temps and control the A/C like stock. At least for my setup. 5.7 LS1s might be different since f body’s came with manual A/C and electric fans. Tried using a F body tune as a base and segment swapped the trans and engine settings and had the same result. Living in Cali I obviously wanted my A/C, so to solve this problem I’m using a thermostat to control when the fans come on. I used a 2001 truck tune to keep my A/C. Thermostat works perfect. Got one for each fan and they work with A/C too. If anyone can find a 6.0 4L80e DBC 2wd tune that can control MANUAL A/C and electric fans correctly, I would really appreciate a copy of the
bin. Trust me, it’s a lot harder to find than you think. Without HPTuners at least. Even with them, I couldn’t find a tune. Until I find the proper .bin, it works for now. Anyway, here’s how I wired the A/C to keep the stock controls working.

Stock LT1 PCM pin outs to LS PCM

Black Connector
Pin #1 - A/C Request - Goes to Red Pin#17
Pin #21 A/C Clutch Status - Red Pin#18

Blue Connector
Pin #8 - A/C Clutch Relay - Red Pin#43
Pin #12 - A/C Pressure Sensor - Red Pin#14


Now on the high pressure switch plug (the one going into the condenser line), there are 3 wires that you have to connect. Gray, Red/Black, and Black. If you wired the pin outs from above first, then you’re really only hooking up the gray wire to 5V ref.

Pic is for reference. Stock Wire colors are different
View attachment 198517
Gray Wire - 5V ref - Goes to Blue Pin#45

Black wire - Ground- Already grounded through stock harness ground as long as you don’t cut it. If cut Blue Pin#60

Red/Black Wire - Already mentioned above. It is the A/C pressure signal and goes to Red Pin#14

Last thing to connect is the vacuum line coming out of the stock harness to the LS intake. Some people may over look that because they have no idea what the hose is for. It is on passenger side towards rear of engine going into intake, incase anyone didn’t know. It’s the only vacuum line coming out the wiring harness. Everything else related to the A/C can be kept as is, assuming you are using the stock HD6 compressor. If not, you just have to splice into clutch wiring for w/e compressor you’re running. Stripping off all the tape and loom off the stock harness first, I was able to trace out the stock wiring for the A/C and didn’t have to cut any of the pigtails off, so this made it pretty easy to hook everything up. This is how I wired up everything and it’s working perfect and blowing cold.

Edit: 7/24/2021
After ALOT of research, I found out that you can use the 2002 tune to control everything properly, as long as you still use a f body tune as a base, and make sure to ground the pressure sensor low reference(ground) properly! The ground within the harness is not good enough. Also make sure your tuner changes the “A/C type” in your tune to “analog”. Then everything will work as it should and cycle properly based on system pressure, just like a stock b body

The ground within the harness is not good enough? So add a ground to this wire?

 

[beking32]

Trucks are wired like this

View attachment 200109
But if you want your A/C and e-fans to work properly, and cycle as it should, you need to wire it like this as stated above, and use a camaro or firebird tune as a basetune. If u have a truck tune and don’t care about the compressor cycling, just ground pin #55 on the red connector, along with connecting all the proper connections, such as A/C request and relay ground, and the compressor will kick on. It just won’t cycle as it should, or activate the 2nd fan based on pressure. You need a f body base tune in order to control the A/C and e- fans off a pressure SENSOR, not SWITCH, like a stock b body

View attachment 200110
[/QUOTE

Yea I should’ve clarified more on this. So to run the a/c with the stock controls, using an f body base tune, with a/c type set to “analog”, wire the pressure switch as follows

High pressure switch
Gray wire - blue - pin 45 : 5V reference

Red/black - red - pin 14 : pressure signal

Black - blue - pin 60 : ground—


Now pin 60, you can ground using a pin at the pcm that isn’t being used (egr solenoid ground), or grounding to frame works as well. If you don’t have a/c type set to “analog” and have “analog cycling”, like in a truck tune. You can ground pin 55 in the red connector to make the compressor kick on, but then it won’t run the fans based off of pressure, temp and speed. Good temporarily until you can get the proper tune if you can’t wait to run a/c. But for sure hook up other a/c wires as follows

A/c Request - blue wire - red -pin 17

Ac clutch enable - green - red pin 18

A/c relay - green/white - red pin 43

You have to make sure you have the correct wire coming from the stock lt1 harness to make this work. Pin outs for that are on lt1swap.com, and I have them identified above as well. All these pin outs are going to an LS red/blue pcm only. Red/green and up is different and a little more complicated but can be done.

thanks I will try it tomorrow and let you know

 

[beking32]

Yea I should’ve clarified more on this. So to run the a/c with the stock controls, using an f body base tune, with a/c type set to “analog”, wire the pressure switch as follows

High pressure switch
Gray wire - blue - pin 45 : 5V reference

Red/black - red - pin 14 : pressure signal

Black - blue - pin 60 : ground—


Now pin 60, you can ground using a pin at the pcm that isn’t being used (egr solenoid ground), or grounding to frame works as well. If you don’t have a/c type set to “analog” and have “analog cycling”, like in a truck tune. You can ground pin 55 in the red connector to make the compressor kick on, but then it won’t run the fans based off of pressure, temp and speed. Good temporarily until you can get the proper tune if you can’t wait to run a/c. But for sure hook up other a/c wires as follows

A/c Request - blue wire - red -pin 17

Ac clutch enable - green - red pin 18

A/c relay - green/white - red pin 43

You have to make sure you have the correct wire coming from the stock lt1 harness to make this work. Pin outs for that are on lt1swap.com, and I have them identified above as well. All these pin outs are going to an LS red/blue pcm only. Red/green and up is different and a little more complicated but can be done.

Thank you I got it working. Grounding pin 55 did for me. Have some koolaid on me.

 

[beking32]

That’s great! But remember, grounding it that way should just be temporary and mostly to see if your compressor is working and all your other wiring is correct. Best thing to do is have a tuner use a f body base file and then work from there. That way you can really use the pressure sensor and run the fans and compressor correctly based off of actual pressure. Also, I used pin 60 on the blue connector because it was an empty low reference coming from PCM. Your harness might be different, but definitely find an empty low reference spot for the sensor.

Yes I used pin 60 also for sensor ground. All I have to do now is find a person who does it in Dallas area.