Need A/C Wiring Help On '94 Sierra LS Swap
09-22-2018, 02:46 PM
#1
Need A/C Wiring Help On '94 Sierra LS Swap Like the title says.. I'm working on a '94 GMC Z-71 LS swap project and I'm trying to get the A/C working. Vehicle is running a Speartech stand alone wiring harness with a 411 PCM. All factory A/C connections are present, and all pressure switches have been tested and are working. The system is charged with freon as of yesterday. We had to run a 12V+ power source to the green wire on the compressor to manually engage the clutch to fill the system. I have found, and tested the A/C relay (it's mounted behind the glove box door on top of the suitcase) and it is working. It receives the signal from the HVAC control unit.
At this point it appears that the factory 1994 PCM (under the glove box above passengers feet) is responsible for cycling, or running, the A/C. I say this because I back-traced the DK. GREEN wire from the compressor directly back to that PCM. I'm not sure how to move those controls over to the new 411 PCM, or if that is even possible? Or should I leave the factory A/C wiring attached to the old PCM and try and figure out why it's not turning the compressor on?
If anyone has any advise, or can point me in the right direction, I would sincerely appreciate it! I have EVERYTHING else on the truck working perfectly and it's just down to making the A/C cycle/run. HELP!
At this point it appears that the factory 1994 PCM (under the glove box above passengers feet) is responsible for cycling, or running, the A/C. I say this because I back-traced the DK. GREEN wire from the compressor directly back to that PCM. I'm not sure how to move those controls over to the new 411 PCM, or if that is even possible? Or should I leave the factory A/C wiring attached to the old PCM and try and figure out why it's not turning the compressor on?
If anyone has any advise, or can point me in the right direction, I would sincerely appreciate it! I have EVERYTHING else on the truck working perfectly and it's just down to making the A/C cycle/run. HELP!
09-22-2018, 05:42 PM
#2
Okay guys.. I've spent the last several hours scouring the web looking for how to do this. I think it is going to be one of those cases where it is so simple than no one has simply taken the time to sit down and detail how to do it..
So far I've learned there are FIXED and SERIAL compressors. Some need a pressure switch, some do not. Depending on what type of hardware is used may require a segment swap, and/or other changes to the tune.
I'm now off to look at wiring diagrams for a 1994 Sierra and see if I can figure out exactly how GM accomplished this. Maybe from there I'll realize how to tie in my existing 411 connections (of which there are only 4 wires). Seems simply right?
So far I've learned there are FIXED and SERIAL compressors. Some need a pressure switch, some do not. Depending on what type of hardware is used may require a segment swap, and/or other changes to the tune.
I'm now off to look at wiring diagrams for a 1994 Sierra and see if I can figure out exactly how GM accomplished this. Maybe from there I'll realize how to tie in my existing 411 connections (of which there are only 4 wires). Seems simply right?
09-22-2018, 05:57 PM
#3
So are you at the point to where you think it should work and it isn't?
If so Tap on the cycling switch mounted on the drier, when you think it should be working.
that and try just moving the wire connector at that same point, lots of people would
open the connection with their hot light trying to diagnose them, can't tell you how many
switches and pigtails I replaced.
I worked at a chevrolet dealership when those thing were new, and that was very common.
If so Tap on the cycling switch mounted on the drier, when you think it should be working.
that and try just moving the wire connector at that same point, lots of people would
open the connection with their hot light trying to diagnose them, can't tell you how many
switches and pigtails I replaced.
I worked at a chevrolet dealership when those thing were new, and that was very common.
09-22-2018, 07:28 PM
#4
Appreciate the input. At this point, I'm still tied to the old, original, 1994 computer with the A/C. I think I'm going to just re-reoute all wiring, and switch wiring, over to the 411 PCM. I think that is the best route to take at this point. As long as I can get all of the sensors tied to the 411 PCM, I think it should work as factory. I will probably just put a new relay under the hood for the A/C Clutch Relay and disable the factory A/C clutch relay which is on top of the suitcase inside the cab. Then the only wire I will need from inside the cab is the lt. blue wire coming from the HVAC control A/C button. I did find a wiring diagram for a 2000 Chevrolet Silverado and it shows 3 switches; 1. High pressure recirculation switch. 2. Low pressure switch. 3. High pressure switch. I'm not sure yet if my 1994 has 3 switches but I will check tomorrow. If all 3 are there, I will then have to identify them, and then route their wiring over to the 411 PCM independently until everything is hooked up.
I'm sure there is an easier way to get it working than this, but nothing I ever do is easy. Might as well jump in with both feet and tie it all to the 411 PCM and hopefully all issues will be behind me.
At this point, in reality, it's just 3 pressure switches, and one relay that I need to get set up with all wiring running back to where it needs to be.. Can't be that difficult right? Ha ha ha!
I'm sure there is an easier way to get it working than this, but nothing I ever do is easy. Might as well jump in with both feet and tie it all to the 411 PCM and hopefully all issues will be behind me.
At this point, in reality, it's just 3 pressure switches, and one relay that I need to get set up with all wiring running back to where it needs to be.. Can't be that difficult right? Ha ha ha!
09-23-2018, 01:29 PM
#6
That's a great looking truck! If you are going 6-0, I hope you are going with a 4L80E transmission at the same time.
On this truck, I bought it as a semi-finished project. The LS was already in it, and it did start and drive. However, I had to re-do every wire on the engine, to include shortening or lengthening about 80% of the wires going to the PCM to get everything neat & tidy. New battery cables. Ground engine to frame. Ground body to frame/engine. Fixed a bunch of electrical issues and now I'm moving on to A/C. After A/C, I need to work further on the 4x4 actuator on the front differential. I found some loose wires and did some research and thought I had them hooked up correctly. I can hear it clicking and if you put your hand on it you can feel it click inside but it won't go into 4x4. I will have to tackle that next and get it sorted out. Then..... I'm not sure the PCM in the truck has the 4 Lo files in it.. Looks like it might be a 2WD tune.. So, I may need to flash the PCM with a 4x4 tune.
The truck is in remarkable shape.. Never wrecked. Interior is damn near flawless. The dash is in factory new condition with no cracks ANYWHERE. This truck as I got it is in better shape than any other truck of it's age that I have ever seen. I got very lucky to have found it as it's a cream-puff. I plan on ironing out every little detail until it all works as factory.
On this truck, I bought it as a semi-finished project. The LS was already in it, and it did start and drive. However, I had to re-do every wire on the engine, to include shortening or lengthening about 80% of the wires going to the PCM to get everything neat & tidy. New battery cables. Ground engine to frame. Ground body to frame/engine. Fixed a bunch of electrical issues and now I'm moving on to A/C. After A/C, I need to work further on the 4x4 actuator on the front differential. I found some loose wires and did some research and thought I had them hooked up correctly. I can hear it clicking and if you put your hand on it you can feel it click inside but it won't go into 4x4. I will have to tackle that next and get it sorted out. Then..... I'm not sure the PCM in the truck has the 4 Lo files in it.. Looks like it might be a 2WD tune.. So, I may need to flash the PCM with a 4x4 tune.
The truck is in remarkable shape.. Never wrecked. Interior is damn near flawless. The dash is in factory new condition with no cracks ANYWHERE. This truck as I got it is in better shape than any other truck of it's age that I have ever seen. I got very lucky to have found it as it's a cream-puff. I plan on ironing out every little detail until it all works as factory.
09-26-2018, 08:04 AM
#7
TECH Addict
I used the factory control to run the a/c on my 1992. I connected to the 411 pcm so the motor knows when the a/c is on bumps idle and increases air since the a/c compressor on those trucks pull some power. I am pretty sure the only switch on that a/c is a low pressure switch. On pcm connectors red connector pin 17 which is a/c request i connected to compressor 12v so 411 pcm knows the a/c is on. I also grounded red connector pin 55 so the pcm knows the a/c has pressure. If you install a pressure switch to the a/c you would connect that to pin 55. You can set it up so the 411 pcm controls the a/c not the trucks pcm.You will just have to wire it like the 2000 pcm .
Trending Topics
09-26-2018, 08:08 AM
#8
TECH Addict
Ls1truck.com has a lot of good info on your swap you just have to do some searching. Since yours is a 1998 i have read you just need to change 10 wires on harness pin connectors and you can use your stock harness to run everything with a 411 pcm.
09-26-2018, 07:50 PM
#9
Mine is actually a 1994. I got all of the wires swapped over EXCEPT the wire coming from the HVAC control module. I will go to LS1truck and check there to see how everyone else is doing it. I also found out today the alternator is no good. Cold start it holds 14.2V, but then quickly starts dropping voltage as it builds heat.. After 5 minutes of idling it dips down into the 8's, and then bounces back up to the 12's. So, I pulled the old alt today and will install a remanned unit tomorrow.
So far, this is what I have run;
Low Pressure switch, 2 wires, 1 wire run to (-) Ground. The 2nd wire run back to the PCM @ RED 55.
High Pressure Switch, 2 wires, 1 Currently run to PCM @ RED 17. The 2nd wire *MAYBE IS SUPPOSED TO CONNECT TO HVAC CONTROLLER?
High Pressure Recirculation Switch, 2 wires, 1 wire run to (-) Ground, the 2nd wire run back to the PCM @ RED 11 So, my diagram shows that the wire coming out of RED 11 actually passes through the FUSE BLOCK UNDERHOOD. No idea why it passes through the fuse block. If 1 leg of this switch connects to ground, how can the other leg get 12V+???
I've got the Compressor clutch relay wired such that RED 43 triggers the relay (-) GROUND, to allow voltage to pass through the relay to the compressor clutch
Today, I got it all wired up except the 2nd wire for the high pressure switch. We started the engine and then tried grounding that wire-NOTHING. Then we tried 12V+ at that wire-still nothing. I went back and checked the low pressure, and the high pressure, switch and they have continuity. The HIGH PRESSURE RECIRCULATION switch DOES NOT have continuity.
It's obvious I still have much reading, and research, to do. Off to the forums! Wish me luck!
So far, this is what I have run;
Low Pressure switch, 2 wires, 1 wire run to (-) Ground. The 2nd wire run back to the PCM @ RED 55.
High Pressure Switch, 2 wires, 1 Currently run to PCM @ RED 17. The 2nd wire *MAYBE IS SUPPOSED TO CONNECT TO HVAC CONTROLLER?
High Pressure Recirculation Switch, 2 wires, 1 wire run to (-) Ground, the 2nd wire run back to the PCM @ RED 11 So, my diagram shows that the wire coming out of RED 11 actually passes through the FUSE BLOCK UNDERHOOD. No idea why it passes through the fuse block. If 1 leg of this switch connects to ground, how can the other leg get 12V+???
I've got the Compressor clutch relay wired such that RED 43 triggers the relay (-) GROUND, to allow voltage to pass through the relay to the compressor clutch
Today, I got it all wired up except the 2nd wire for the high pressure switch. We started the engine and then tried grounding that wire-NOTHING. Then we tried 12V+ at that wire-still nothing. I went back and checked the low pressure, and the high pressure, switch and they have continuity. The HIGH PRESSURE RECIRCULATION switch DOES NOT have continuity.
It's obvious I still have much reading, and research, to do. Off to the forums! Wish me luck!
09-26-2018, 10:17 PM
#10
Low Pressure switch, 2 wires, 1 wire run to (-) Ground. The 2nd wire run back to the PCM @ RED 55.
High Pressure Switch, 2 wires, 1 Currently run to PCM @ RED 17. The 2nd wire *MAYBE IS SUPPOSED TO CONNECT TO HVAC CONTROLLER? Yes, this is the A/C request wire, so the 12v wire coming out of the HVAC controller should connect to it to power it up whenever the A/C is turned on.
High Pressure Recirculation Switch, 2 wires, 1 wire run to (-) Ground, the 2nd wire run back to the PCM @ RED 11 So, my diagram shows that the wire coming out of RED 11 actually passes through the FUSE BLOCK UNDERHOOD. No idea why it passes through the fuse block. If 1 leg of this switch connects to ground, how can the other leg get 12V+??? Do you have the high pressure recirculation switch in you're A/C line? I didn't think a '94 would have it. You don't need it on a swap, just the high pressure switch in the back of the compressor and the low pressure switch on the accumulator is all you need for it to work. Where that wire goes through the fuse box is just a pass through, it doesn't get any power from it.
I've got the Compressor clutch relay wired such that RED 43 triggers the relay (-) GROUND, to allow voltage to pass through the relay to the compressor clutch
Today, I got it all wired up except the 2nd wire for the high pressure switch. We started the engine and then tried grounding that wire-NOTHING. Then we tried 12V+ at that wire-still nothing. I went back and checked the low pressure, and the high pressure, switch and they have continuity. The HIGH PRESSURE RECIRCULATION switch DOES NOT have continuity. If you are checking for continuity on just the switch, then it wont have it until the pressure reaches a certain amount, but again, you don't really need it for the system to work.
High Pressure Switch, 2 wires, 1 Currently run to PCM @ RED 17. The 2nd wire *MAYBE IS SUPPOSED TO CONNECT TO HVAC CONTROLLER? Yes, this is the A/C request wire, so the 12v wire coming out of the HVAC controller should connect to it to power it up whenever the A/C is turned on.
High Pressure Recirculation Switch, 2 wires, 1 wire run to (-) Ground, the 2nd wire run back to the PCM @ RED 11 So, my diagram shows that the wire coming out of RED 11 actually passes through the FUSE BLOCK UNDERHOOD. No idea why it passes through the fuse block. If 1 leg of this switch connects to ground, how can the other leg get 12V+??? Do you have the high pressure recirculation switch in you're A/C line? I didn't think a '94 would have it. You don't need it on a swap, just the high pressure switch in the back of the compressor and the low pressure switch on the accumulator is all you need for it to work. Where that wire goes through the fuse box is just a pass through, it doesn't get any power from it.
I've got the Compressor clutch relay wired such that RED 43 triggers the relay (-) GROUND, to allow voltage to pass through the relay to the compressor clutch
Today, I got it all wired up except the 2nd wire for the high pressure switch. We started the engine and then tried grounding that wire-NOTHING. Then we tried 12V+ at that wire-still nothing. I went back and checked the low pressure, and the high pressure, switch and they have continuity. The HIGH PRESSURE RECIRCULATION switch DOES NOT have continuity. If you are checking for continuity on just the switch, then it wont have it until the pressure reaches a certain amount, but again, you don't really need it for the system to work.
09-27-2018, 07:24 PM
#11
Success! Well, partial success.. I got everything wired up and the compressor kicks in.. The only problem I have now is that the HVAC head unit is NOT putting out 12 volts. I actually pulled it from the dash and tied directly into the BLUE A/C REQUEST wire on the back of the controller and it's only putting out 5V.. Not enough to even trigger a relay (yes I tried). I disassembled the head unit and can see damaged resistors on the circuit board. When I say damaged I mean they got so hot they burned off their identifying color bands! One of them looks like it swole up in a circular fashion and no longer has the same shape as it's neighboring resistors. So, I've ordered a new HVAC controller. Everything under the hood is PERFECT. I applied 12V to the 2nd leg of the high pressure switch and instantly the compressor kicks on. Now that I have an understanding of how the system works, I can see how easy it would be to do a "stand alone" A/C harness... Thanks for hanging in there with me while I figured this out.
I also got a 145 Amp alternator, and a #4 gauge charge wire between alternator and battery, installed today. It holds 14.4 even with both cooling fans, and the A/C on MAX, at idle. Jumps up to 14.5 with a little gas pedal. So, slowly I'm chipping away at the issues. I did have to evac the A/C system today though.. The high pressure switch O-ring is leaking at the compressor body. Luckily I charged the system with dye and I could see the dye coming from around the high pressure switch today. Each day I resolve one issue, and the truck throws 2 new ones at me. It's a cycle.
I also got a 145 Amp alternator, and a #4 gauge charge wire between alternator and battery, installed today. It holds 14.4 even with both cooling fans, and the A/C on MAX, at idle. Jumps up to 14.5 with a little gas pedal. So, slowly I'm chipping away at the issues. I did have to evac the A/C system today though.. The high pressure switch O-ring is leaking at the compressor body. Luckily I charged the system with dye and I could see the dye coming from around the high pressure switch today. Each day I resolve one issue, and the truck throws 2 new ones at me. It's a cycle.
09-28-2018, 06:51 PM
#12
Found out today that the O-ring for the high pressure switch is all that was leaking. I replaced the O-ring, put the old switch back in, vacuumed it out and it held 25 in. lb. of vacuum for over 20 minutes. Re-charged the system with fresh freon and everything seems to be holding. Waiting on the remanned HVAC controller to get here.
09-30-2018, 02:53 PM
#14
Dime-I'm not 100% sure what it is you need. Break down of finished wiring? A/C related? Sure, that's easy enough;
LOW PRESSURE SWITCH (mounted on the accumulator/dryer) 2 wires-1 leg goes to GROUND (-), the 2nd wire goes to RED 55
HIGH PRESSURE SWITCH (mounted on compressor body) 2 wires-1 wire gets 12V+ from the dash mounted A/C controller, 2nd wire goes to RED 17
HIGH PRESSURE RECIRCULATION SWITCH (mounted on the high pressure hose) 2 wires, 1 goes to GROUND (-), 2nd wire goes to RED 11
Then, the last wire-RED 43 from the PCM is the GROUND (-) wire from the PCM which grounds the relay for the compressor clutch. Yes, it's really that simple. This is the TRUCK set up. Please be certain you have matching harness, components, and operating system. The F-body uses a SERIAL compressor that also needs an actual pressure sensor in order for it to work correctly. It also uses a different operating system in the PCM. Just be CERTAIN whether you are going TRUCK, or F-body/Corvette, set-up and use all matching components-compressor, wiring harness, necessary switches, and operating system.
LOW PRESSURE SWITCH (mounted on the accumulator/dryer) 2 wires-1 leg goes to GROUND (-), the 2nd wire goes to RED 55
HIGH PRESSURE SWITCH (mounted on compressor body) 2 wires-1 wire gets 12V+ from the dash mounted A/C controller, 2nd wire goes to RED 17
HIGH PRESSURE RECIRCULATION SWITCH (mounted on the high pressure hose) 2 wires, 1 goes to GROUND (-), 2nd wire goes to RED 11
Then, the last wire-RED 43 from the PCM is the GROUND (-) wire from the PCM which grounds the relay for the compressor clutch. Yes, it's really that simple. This is the TRUCK set up. Please be certain you have matching harness, components, and operating system. The F-body uses a SERIAL compressor that also needs an actual pressure sensor in order for it to work correctly. It also uses a different operating system in the PCM. Just be CERTAIN whether you are going TRUCK, or F-body/Corvette, set-up and use all matching components-compressor, wiring harness, necessary switches, and operating system.