A/C wiring? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bigguy · 01-30-2011, 07:55 PM

Does anyone know how to wire the A/C using a Painless harness?

usmcchevy · 01-30-2011, 09:50 PM

No real help here, but I am just going to wire mine however my AC kit says to, eliminating the PCM from the equation.

**TR65** · 01-30-2011, 10:44 PM

BigGuy,

I don't have a painless harness, I am using the stock one. But I am hooking up my Vintageair AC and using the ECM to control the compressor and fans.
I have a 2005 6L LS2 (E40 ECM).

There is a signal wire to the ECM where the AC system asks for the compressor to run. The Ecm controls the compressor clutch relay thru another wire. There is a pressure transducer mounted in the high pressure line coming out of the compressor. There are two wires in the harness going to it. The ECM uses this pressure signal to control the electric fans according to a lookup table. So the fans don't have to come on full blast when the AC comes on. They come on as required by the pressure in the system. The pressure sensor also serves as a safety switch to protect the compressor in case of too high or too low system pressure.

I am in the process of hooking it up now but I am not finished.

TR

usmcchevy · 01-30-2011, 11:08 PM

TR65, Thanks for the info. I never knew the PCM could do that................but my engine didn't come from the factory with E fans, so I guess thats why. I'll have look into this more when I get my AC system.

**Clyde65** · 01-31-2011, 11:20 AM

I have an Old Air Products Ac system and hooked up the stock LS compressor to it ( wired around the ls harness, no efan PCM) and it works great.

87chevy.com · 02-02-2011, 01:23 AM

* cough * found this schematic on the net somewhere
C2 pin 43 is the ground control for the relay that will controll the a/c compressor relay. you will need to make your own relay since painless is retarded and didnt include it for you. Simple enough to add a relay to their block though.
just wire the relay up like in the schematic in the upper left.

man, I forgot how i wired mine... I will look at it tomarrow afternoon and reply. I dont remember how I powered up the relay... I dont remember cutting any of the a/c wiring... I think there was a terminal on the firewall that was the compressor 12v wire... im almost sure now, thats what i used to power up the relay. That away it uses the factory low pressure circuit w/o cutting any of that stuff.

There was also another wire that should be grounded ( i will have to double check on my truck.... dont want to tell you anything wrong, but im pretty sure.., C2 pin 11.... unless you install a fitting and run the factory HIGH pressure sensor. If you leave this wire open, not connected your factory a/c will not work.. took me forever to find this schematic.... This schcematic is for an 2002 pcm.. probally the same for others.. what year are you working with.
clint

bigguy · 02-02-2011, 12:43 PM

Its a 2000 pcm from a tahoe

87chevy.com · 02-02-2011, 08:29 PM

i looked at the wire I grounded, but its all taped up. I will check it out this weekend.
clint

bigguy · 02-07-2011, 07:03 PM

Much appreciated.

Custom 68 · 02-23-2011, 02:27 PM

sorry guys just now saw this. on mine I just used the factory (the 1968 truck) green wire for the AC on. The painless harness does have a wire to hook up to this also but with it hooked up i never could tell it did anything. I thought maybe it woule "idle it up" or turn on the e-fans but didnt seem to do anything. I left it unhooked. My AC works just like the stock or factory did in 1968. I think the only thing really required is the compressor to see a 12 volt causing it to kick the clutch on.

87chevy.com · 02-24-2011, 02:24 AM

Quote:

Originally Posted by Custom 68

sorry guys just now saw this. on mine I just used the factory (the 1968 truck) green wire for the AC on. The painless harness does have a wire to hook up to this also but with it hooked up i never could tell it did anything. I thought maybe it woule "idle it up" or turn on the e-fans but didnt seem to do anything. I left it unhooked. My AC works just like the stock or factory did in 1968. I think the only thing really required is the compressor to see a 12 volt causing it to kick the clutch on.

That setup works BUT the ecu does not know the compressors on and the engine rpm will go down, hesitate and will not turn off if you decide to WOT .. Why painless dint spend 5 extra bucks and add the required relay and a few extra wires... Same reason toyota didn't use the brake pedal switch to deactivate the deadly throttle body or gas pedal problem... Answer: no body knows
clint
Posted via Mobile Device

01-30-2011, 07:55 PM	#1
bigguy Registered User Join Date: Jun 2010 Location: Northern VA Posts: 89	A/C wiring? Does anyone know how to wire the A/C using a Painless harness?

01-30-2011, 09:50 PM	#2
usmcchevy Has more rust than truck... Join Date: Apr 2005 Location: Ivanhoe, MN Posts: 2,421	Re: A/C wiring? No real help here, but I am just going to wire mine however my AC kit says to, eliminating the PCM from the equation. __________________ 1972 Custom/10 SWB, 4.8/4l80e Build thread LSx Swap FAQ index

01-30-2011, 10:44 PM	#3
TR65 Senior Member Join Date: Nov 2007 Location: Greenville, SC Posts: 873	Re: A/C wiring? BigGuy, I don't have a painless harness, I am using the stock one. But I am hooking up my Vintageair AC and using the ECM to control the compressor and fans. I have a 2005 6L LS2 (E40 ECM). There is a signal wire to the ECM where the AC system asks for the compressor to run. The Ecm controls the compressor clutch relay thru another wire. There is a pressure transducer mounted in the high pressure line coming out of the compressor. There are two wires in the harness going to it. The ECM uses this pressure signal to control the electric fans according to a lookup table. So the fans don't have to come on full blast when the AC comes on. They come on as required by the pressure in the system. The pressure sensor also serves as a safety switch to protect the compressor in case of too high or too low system pressure. I am in the process of hooking it up now but I am not finished. TR __________________ 1965 C10 SWB Fleet Two owner LS2 Swap Thread http://67-72chevytrucks.com/vboard/s...d.php?t=413880

01-30-2011, 11:08 PM	#4
usmcchevy Has more rust than truck... Join Date: Apr 2005 Location: Ivanhoe, MN Posts: 2,421	Re: A/C wiring? TR65, Thanks for the info. I never knew the PCM could do that................but my engine didn't come from the factory with E fans, so I guess thats why. I'll have look into this more when I get my AC system. __________________ 1972 Custom/10 SWB, 4.8/4l80e Build thread LSx Swap FAQ index

01-31-2011, 11:20 AM	#5
Clyde65 1965 Chevy C10, 2005 4.8L/4l60 Join Date: Aug 2004 Location: DFW Texas Posts: 8,546	Re: A/C wiring? I have an Old Air Products Ac system and hooked up the stock LS compressor to it ( wired around the ls harness, no efan PCM) and it works great. __________________ Clyde65 Rebuild of Clyde http://67-72chevytrucks.com/vboard/s...84#post8338184 69 Aristocrat Lo Liner build http://67-72chevytrucks.com/vboard/s...84#post7561684 *support our troops!*

02-02-2011, 01:23 AM	#6
87chevy.com BMW & ASE Master Certified Join Date: Feb 2004 Location: Houston, Texas Posts: 1,266	Re: A/C wiring? * cough * found this schematic on the net somewhere C2 pin 43 is the ground control for the relay that will controll the a/c compressor relay. you will need to make your own relay since painless is retarded and didnt include it for you. Simple enough to add a relay to their block though. just wire the relay up like in the schematic in the upper left. man, I forgot how i wired mine... I will look at it tomarrow afternoon and reply. I dont remember how I powered up the relay... I dont remember cutting any of the a/c wiring... I think there was a terminal on the firewall that was the compressor 12v wire... im almost sure now, thats what i used to power up the relay. That away it uses the factory low pressure circuit w/o cutting any of that stuff. There was also another wire that should be grounded ( i will have to double check on my truck.... dont want to tell you anything wrong, but im pretty sure.., C2 pin 11.... unless you install a fitting and run the factory HIGH pressure sensor. If you leave this wire open, not connected your factory a/c will not work.. took me forever to find this schematic.... This schcematic is for an 2002 pcm.. probally the same for others.. what year are you working with. clint Attached Images __________________ 1987 Silverado - L83 5.3 w/ 6L80e ,A/C,P/W,P/L,TILT, HID projectors, Wilwood C-10 Pro Spindles w/ 2018 silverado front brakes & C-5 Corvette Rear Disc Brakes 1999 BMW 528i - 5.7 LS1 w/ 4l60e, Ford 8.8 IRS w31 spline posi & FX-r projector retrofit New project: 2006 BMW x5 6cyl AWD to L83 6l80e 4wd to 2WD / RWD A poor man buy's it twice finally got my domain name back, 87chevy.com.... site rework in progress

02-02-2011, 12:43 PM	#7
bigguy Registered User Join Date: Jun 2010 Location: Northern VA Posts: 89	Re: A/C wiring? Its a 2000 pcm from a tahoe

02-02-2011, 08:29 PM	#8
87chevy.com BMW & ASE Master Certified Join Date: Feb 2004 Location: Houston, Texas Posts: 1,266	Re: A/C wiring? i looked at the wire I grounded, but its all taped up. I will check it out this weekend. clint __________________ 1987 Silverado - L83 5.3 w/ 6L80e ,A/C,P/W,P/L,TILT, HID projectors, Wilwood C-10 Pro Spindles w/ 2018 silverado front brakes & C-5 Corvette Rear Disc Brakes 1999 BMW 528i - 5.7 LS1 w/ 4l60e, Ford 8.8 IRS w31 spline posi & FX-r projector retrofit New project: 2006 BMW x5 6cyl AWD to L83 6l80e 4wd to 2WD / RWD A poor man buy's it twice finally got my domain name back, 87chevy.com.... site rework in progress Last edited by 87chevy.com; 02-02-2011 at 08:30 PM.

02-07-2011, 07:03 PM	#9
bigguy Registered User Join Date: Jun 2010 Location: Northern VA Posts: 89	Re: A/C wiring? Much appreciated.

02-23-2011, 02:27 PM	#10
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,939	Re: A/C wiring? sorry guys just now saw this. on mine I just used the factory (the 1968 truck) green wire for the AC on. The painless harness does have a wire to hook up to this also but with it hooked up i never could tell it did anything. I thought maybe it woule "idle it up" or turn on the e-fans but didnt seem to do anything. I left it unhooked. My AC works just like the stock or factory did in 1968. I think the only thing really required is the compressor to see a 12 volt causing it to kick the clutch on. __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

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