Ok so when you cut the old computer harnes out you cut the AC clutch wire and the high pressure switch wire off because it goes into the 3rd gen computer. So what have you guys done to get your AC hooked up correctly? Any help is great guys as i am going to start the install this weekend. Thanks

 

There's more than one way to skin this cat, from what I understand (and I don't have mine up and running yet).

I had never heard the 3rd gen AC signal went through the computer, but I could be wrong there. I'm familiar with '82-'86, and they do not go through the computer.

Can we assume you're using the 4th gen/LS1 AC compressor?

If you retain the 4th gen pressure switch (which is a combined high and low pressure unit) and you're running the 4th gen harness, all you need is to give the PCM the AC request signal (Pin F in the C230 connector). The PCM takes it from there, including the radiator fan switching.

Or, you can retain the 3rd gen pressure switch and route the compressor clutch power in series with the low pressure switch. But, you won't have a high side pressure switch that way, because the high side switch is part of the 3rd gen compressor.

 

Unless something drastically changed after 87....the 3rd gen a/c doesnt go into the 3rd gen ECM at all. The HVAC is sort of on its own harness, self contained. The compressor clutch is in series with the low and high pressure switches. Only if those two switches are closed will the clutch engage.

Im gonna play the role of the "bad guy" a little here and highly recommend you search. Here, and over on ls1tech. I KNOW there are threads upon threads about hooking up a/c...whether you are using all thirdgen parts, 4th gen compressor, or 100% 4th gen system. Ive personally probably posted 1/2 a dozen times on what to do with wiring and such.

The info is around! Check my threads/posts specifially if you want. Might help put you on the right track. It'll also give you other options for a/c hookup.

Good luck!

J.

 

Ok well i cut the three plugs going into the 3rd gen computer and the other plug i think its the C207 and now my green wire to my compressor clutch and the grey wire to my low pressure switch are not connected to anything. I checked the small plug that i think is the C207 and the wires going to it dont match my AC wires so they had to go into the computer. Does anyone have a simplified diagram that would show me how to reconnect these?

 

It's in the bundle of wires that comes through the firewall behind the passenger side head.

First rule of engine swap wiring: Don't cut anything until you know what you need to do to get everything functioning.

 

https://www.thirdgen.org/forums/ltx-...9-5-3-t56.html

Skip to post #35

 

That shows how to get the PCM to command the AC clutch, but it doesn't show how to get the HVAC control inside the car to tell the PCM to turn on the AC.

Or am I missing what the original question was?

 

I'll draw up a better diagram tonight when I get home of what I did with my car. I had a green wire that came from the HVAC panel in the car and came out to the passenger side firewall, from there I ran it to the LS1 PCM, this is the signal request wire, it sends 12 v to the computer letting it know you want the a/c on. The diagram posted above shows what I did from there. You have to have the 3-wire high pressure switch since you are going through the LS1 computer like I am.

 

http://www.lt1swap.com/pictures/18_ac_comp_controls.gif

The only input from the HVAC head unit goes to R17

http://www.austinthirdgen.org/mkport...F_and_vin8.jpg

Looking at this, could you simply run without any PCM control? HVAC head input strait to the AC clutch?

 

Yes, but the reason I'm letting the pcm handle mine is so that when you turn the a/c on the pcm will pick the engine idle up, its really not that big of s deal but that's the way I want to do mine

 

Follow the LS1 AC method. The Lt grn wire in the HVAC plug is AC control

 

+1, and you are correct

 

 

I am using a 5.3L and the pin outs are different. Anyone have the correct pinouts for the truck harness?

 

The pinouts are the same unless your year is out of the range

 

Nope i pulled the pinouts on LT1Tech and they are not the same. Any ideas?

 

What year truck harness

 

2001

 

I have a reworked 00 truck harness on my LS1. The pinouts are close enough

99-02 did not change
http://www.lt1swap.com/99-02_vortec_pcm.htm

The only difference I see is there is no R18 pin calling the AC clutch. The relay takes care of that anyways

 

Following his diagram, So are you saying that even though the pins are not the same to use them anyways and it will work?

Red pin14= LS1 ECM "AC pressure signal"
Red Pin14= Truck ECM "Not used"

Red pin18= LS1 ECM "AC compressor clutch supply voltage"
Red pin18= Truck ECM "Not used"

Red pin43= Same on both ECM's

Red pin57= Same on both ECM's

Blue pin45= LS1 ECM "5volt referance AC pressure sensor"
Blue pin45= Truck ECM "5volt fuel tank sensor reference"

 

So the trucks dont have the pressure sensor, or the direct call for the AC clutch. They do retain the relay and functions though...

Wire it without them. Its very similar to a non computer controlled AC system



For future reference, 5v ref or common low ref(ppl or blk) is interchangeable across the PCM. The TPS 5v ref can be swapped with MAP 5v ref without consequence or simply tied together at a single pin. The only thing that HAS to be correct is the signal wire. I found that out researching my 0411 harness

So AC pressure 5v can replace the fuel pressure 5v. Wideband guys are loving that when they use the EGR wiring to run the WB controller

Enabling the AC sensor input is something to talk with your tuner about. Cars and trucks used the same PCMs, so changes in pinouts suggests multiple uses or slight variations in the tune

 

Hmmmmm...... I didn't know that about the truck computer and harness, I always thought they were the same, learned something new today.

 

I think I doomed myself by using a Painless harness, all you need in the setup is a single wire going to the ECM? I might have to add the pin, but that should be easy enough.

I currently have no compressor in the car, but I want to get the other electronic components working first, does the heater and fan modes run through the body wiring, and not the computer harness?

 

Thats right

 

In the first diagram on the bottom right coming from the hvac unit, what is the "p110" ??

 

I'm still a little confused with the AC wiring. All I have at the moment on my Tech Rods stand alone harness is a green/white AC signal wire.



With this method the low pressure switch is no longer used?

 

Just for clarification, the light green wire originally going to the switch on the drier gets cut and now is touted to R17?

Where does the darker green wire on the 3 rd gen black 4 pin plug go?

I don't see anything going to the switch on the drier anymore with the wiring methods shown abobe. Do I still use the switch on the drier?

 

Help needed....BUMP

 

Blue Green PCM info,

http://ls1tech.com/forums/conversion...cm-turn-c.html

 

Subscribed

 

 

The stock ECM on a later model 3rd gen does control the AC Compressor operation partially. It doesn't control when it is ON but it doesn't provide an alternate path to ground with a resistor internally to shut it OFF when the RPM or Throttle is at a certain point. Here is the factory wiring diagram showing this: