AC wires

[bark]

Hello was just wondering which AC wires I need in the factory harness

Computer
#14 red/blk circuit 380, refrigerant pressure sensor signal, I assume it will turn on fans, or idle motor up when ac engages


#43 dk green/white circuit 459, compressor clutch relay control, I assume this powers the relay to run the compressor

#80 blk ciruit 2751, low reference ac, no idea what this does??


fuse block
dark green circuit 59, ac compressor supply voltage, should have + when #43 powers it up

Now where do I hook my trucks ac switch into the harness to tell ac to work

[Pyro]

First, what year PCM and what engine is the PCM for? I have schematics for them all, just want to make sure I give you the right info

[bark]

2004 2500 6.0L 4L80e

[ls1nova71]

You're probably not going to be able to make it work through the PCM because there is no A/C request wire, it's run on a serial data line starting in 2003. You'll most likley have to bypass the PCM all together.

[bark]

ya thats what I thought, But if I bypass the pcm what will tell the engine to idle up when the ac comes on?

[ls1nova71]

You will get a very slight engine bog (if that's the right term) but as soon as the PCM sees it, it will automatically compensate for it. I would say it's noticeable but not really all that bad. The only other way yo make it work through the PCM would be to either switch to an older PCM (411) but then you would havve to convert.to DBC. Or you could possibly use the A/c controls out of a 2003 up truck, but in my opinion it'd be more work than it'd be worth.
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[TR65]

Originally Posted by bark

Hello was just wondering which AC wires I need in the factory harness

Computer
#14 red/blk circuit 380, refrigerant pressure sensor signal, I assume it will turn on fans, or idle motor up when ac engages


#43 dk green/white circuit 459, compressor clutch relay control, I assume this powers the relay to run the compressor

#80 blk ciruit 2751, low reference ac, no idea what this does??


fuse block
dark green circuit 59, ac compressor supply voltage, should have + when #43 powers it up

Now where do I hook my trucks ac switch into the harness to tell ac to work

bark,

Here is the way I am running mine (2005 LS2 E40 ECM). The ECM won't control the compressor clutch because the signal comes over the bus from the HVAC control module which we don't have as LS1Nova said. So you use your AC switch to control the AC clutch relay coil. The ECM uses the dk green/white wire to ground the relay coil and fire the relay. Your AC switch can do that when you want AC. The AC clutch relay then should power the dk green wire to operate the AC clutch.

The ECM will control the fans according to a lookup table in the ECM program if you use the refrigerant pressure sensor. It has three wires rd/bk, bk, grey (circuits 2700, 2751, 380). The ECM smartly uses the fans only as necessary based on the high side system pressure.

The only problem then is that the ECM can't cut the clutch off if the system pressure is too high or too low since it is no longer controlling the clutch. So we really need a trinary safety switch in the clutch line.

Here is a pic of the sensor I installed on my compressor block.

Good luck,

TR

[ls1nova71]

Originally Posted by TR65

The ECM will control the fans according to a lookup table in the ECM program if you use the refrigerant pressure sensor. It has three wires rd/bk, bk, grey (circuits 2700, 2751, 380). The ECM smartly uses the fans only as necessary based on the high side system TR

Have you personally tried this and verified that it does actually work? I,ve heard people say that it will work on an LS1, but that's with the older style A/C with the 12v request, but I would like to know for sure that it will work on the serial data type A/C system. I have also heard that along with turning the fans on, it will also bump up the idle, but its all just hear say, as I"ve yet to have someone say they actually did it. I have been thinking of doing this on my 5.3 I'm working on, but don"t want to go through all the trouble if there,s a chance it won't work, would be way easier to just put a fan on the water pump, but
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[TR65]

Originally Posted by ls1nova71

Have you personally tried this and verified that it does actually work? I,ve heard people say that it will work on an LS1, but that's with the older style A/C with the 12v request, but I would like to know for sure that it will work on the serial data type A/C system. I have also heard that along with turning the fans on, it will also bump up the idle, but its all just hear say, as I"ve yet to have someone say they actually did it. I have been thinking of doing this on my 5.3 I'm working on, but don"t want to go through all the trouble if there,s a chance it won't work, would be way easier to just put a fan on the water pump, but
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I put vacuum on my system today, it leaked by the way so I have to find the leak. So I don't know for sure that it will work.

Here is why I think it will work. I started the truck the first time with no AC pressure sensor. Both fans started a few seconds after you started the truck. With the sensor unplugged the ECM evidently thought the system pressure was too high and turned all cooling fans on. I zeroed out the AC fan tables in the ECM to stop that. So I think the ECM controls the AC system pressure independent of an AC request. I should know for sure in a couple of weeks.

One thing I have been thinking about is just hooking up an AC control module and get it to put the AC request on the bus.

TR

[chevydog66]

Interesting. I am eager to get my a/c working on my 72 GMC with 01 6.0 dbc and LS clutch fan. I'll be watching this one.

[ls1nova71]

Originally Posted by TR65

I put vacuum on my system today, it leaked by the way so I have to find the leak. So I don't know for sure that it will work.

Here is why I think it will work. I started the truck the first time with no AC pressure sensor. Both fans started a few seconds after you started the truck. With the sensor unplugged the ECM evidently thought the system pressure was too high and turned all cooling fans on. I zeroed out the AC fan tables in the ECM to stop that. So I think the ECM controls the AC system pressure independent of an AC request. I should know for sure in a couple of weeks.

One thing I have been thinking about is just hooking up an AC control module and get it to put the AC request on the bus.

TR

Ok, I'm still wanting somebody to prove to me that it will work, and since my truck is still in the paint stage, I can wait until you get yours charged. But from what I've read in service manuals, unplugging the pressure sensor should ste a DTC and prevent the A/C from coming on, but it doesn't say whether it would command the fans on. I wish I knew someone with a new enough truck that had electric fans and I would try unplugging the sensor and see what happens, but all I can find are the older clutch fan trucks.

I also thought about hiding the original A/C switch/control module under the dash and then running the '72 switch to it, but there's little to no room under the dash of a factory air '72.

[ls1nova71]

Originally Posted by chevydog66

Interesting. I am eager to get my a/c working on my 72 GMC with 01 6.0 dbc and LS clutch fan. I'll be watching this one.

Your 2001 will have a wire going to the PCM that's labled 'A/C request', if you hook your oriinal A/C switch wire to it and provided you have the pressure sensors hooked up, it will work. After 2003, they went to a serial data line A/C request that makes things tougher.

[chevydog66]

LS1 thanks for the help. Now to get the high mount brackets and hoses.
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[87chevy.com]

There is probally a way in HPtuners to turn the bus to serial... like the tow/haul button.... originally its momentary ground to the BCM, then a bus signal to the PCM .... went into HPtuners and changed the Transmission Shift properties to one switch... wired in a momentary ground using the "set" in the cruise control for tow haul... works like factory tow haul... 2 shift tables... so maybe you can change the same thing in the a/c table? .. after scanning through the options, didnt see any options to change it..
clint

[TR65]

Originally Posted by ls1nova71

Ok, I'm still wanting somebody to prove to me that it will work, and since my truck is still in the paint stage, I can wait until you get yours charged. But from what I've read in service manuals, unplugging the pressure sensor should ste a DTC and prevent the A/C from coming on, but it doesn't say whether it would command the fans on. I wish I knew someone with a new enough truck that had electric fans and I would try unplugging the sensor and see what happens, but all I can find are the older clutch fan trucks.

I also thought about hiding the original A/C switch/control module under the dash and then running the '72 switch to it, but there's little to no room under the dash of a factory air '72.

LS1Nova,

Got my A/C system running today. So I can verify that the ECM (2005 E40)will control the high side system pressure using the fans with no A/C request. I am using the stock table in the ECM. One fan comes on when the system pressure reaches 200 psi and goes off at 150 psi. Running on the highway, plenty of cooling air and no fans come on.

This is just what I wanted except that the ECM can't protect the compressor by releasing the clutch if the pressure goes too high or too low. I am going to have the ECM turn on the check engine light for a system pressure fault. Then I can manually cut the A/C off.

TR

[eagleuh1]

Why not just put a high pressure cutout switch in the hp line. Wire it in series with the lp cutout and ac on switch.

[TR65]

Originally Posted by eagleuh1

Why not just put a high pressure cutout switch in the hp line. Wire it in series with the lp cutout and ac on switch.

Yea, I got a binary safety switch to put in one of the drier ports. It is just a shame that the ECM is programmed to do this and it would be nice to get it to work. Just a nerd thing.

TR

[eagleuh1]

I hear you. Thats why I haven't got my AC working. I wanted to keep my DBW, but it sucked not having AC. Working on it right now. Got to buy a torch and some aluminum brazing rod and a few more fittings. Hopefully this weekend.

[eagleuh1]

Well, have had internet problems last 3 days, so using library computer. Finally got my order placed to Docs blocks for all my AC fittings and hoses. Hopefully soon will have working. Sorry to say though Docs blocks says they will phase out selling to individuals, only dealers in very near future. There goes my local AC fitting supplier with great prices. Can't just walk in the door and talk to their engineers and order the parts in person. I'll be using the stock evap and condensor with 77 Olds accumulator and orifice tube, with stock 2005 trinary switch for the fans and a binary switch for over and under pressure protection. Hope it works. Jim

[Thealien]

eagleuh1 I'll be picking your brain and asking for pictures when you get yours working.

[TR65]

Originally Posted by eagleuh1

Well, have had internet problems last 3 days, so using library computer. Finally got my order placed to Docs blocks for all my AC fittings and hoses. Hopefully soon will have working. Sorry to say though Docs blocks says they will phase out selling to individuals, only dealers in very near future. There goes my local AC fitting supplier with great prices. Can't just walk in the door and talk to their engineers and order the parts in person. I'll be using the stock evap and condensor with 77 Olds accumulator and orifice tube, with stock 2005 trinary switch for the fans and a binary switch for over and under pressure protection. Hope it works. Jim

Sounds like a plan. Good luck and I will be looking for updates. If I can help in any way let me know. I had a pile of burnt, melted, twisted aluminum before I got the brazing down. That is really bad news about Doc's Blocks.

TR

[eagleuh1]

Yeh. I was suprised when I found out they were right down the road. And have a big factory right here in Arkansas. Very high tech facility. And one of the engineers is a brother of my wifes friend. They're very helpfull and friendly when I walked in. Will be sorry to see them go that way. On another note, just to warn you TheAlien, It'll be slim pickens when you go to picken my brains. TR65 looks like the one with the right stuff here. LOL. I got my order delivered today at 1330. Missing the brazing rod. Called them up. Out of stock. Had to go buy something simialar from the weld shop. Melts at 735 instead of 1100*F. Hope it works. I'll post pics when I start. Still have to get an Orifice Tube repair kit. Oreillys lost and can't find the one they saved for me. Today was the guys day off that last handled it. It's been my kind of day.Jim

[chevydog66]

Sorry to bring up this old thread, but I think some of this needs to be a "Sticky" on how to wire and plumb an a/c system on DBW and DBC LS motors. I still have questions.

[solidaxel]

Originally Posted by chevydog66

Sorry to bring up this old thread, but I think some of this needs to be a "Sticky" on how to wire and plumb an a/c system on DBW and DBC LS motors. I still have questions.

............. Yes Please, or did I miss it?

[Gordonr1973]

Another great a/c thread.