The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > General Truck Forums > Engine & Drivetrain > LSx Swaps

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 09-21-2021, 01:31 AM   #1
chev-obsession
Senior Member
 
chev-obsession's Avatar
 
Join Date: Jul 2008
Location: kennewick, WA
Posts: 1,513
AC compressor relay and Trinary switch wiring question

I am wiring in a stock Denso (new replacement) ac compressor, and wiring the compressor with a trinary switch. In the research I’ve gathered on this I think I’ve drawn this correctly. Since this is my first time doing this task I am hoping someone can tell me if I’ve done it right or what I’ve done wrong/you would do instead. Hoping there is people with more experience than what I have in this department before wiring it in so it’s done right the first time.

The company who went through the harness left the green/white wire labeled “AC Compressor” and a grey/black wire labeled “AC Request”. I attached a copy of how the trinary switch manufacture recommends it be installed. I basically replaced the ac thermostat switch with the compressor relay, and using the ac switch in the cab to trigger the relay.

Any help is appreciated
Posted via Mobile Device
Attached Images
  
chev-obsession is offline   Reply With Quote
Old 09-21-2021, 11:51 AM   #2
Davidf
Registered User
 
Join Date: Nov 2014
Location: Austin
Posts: 749
Re: AC compressor relay and Trinary switch wiring question

Where is the ECM in your diagram? You want the ECM to control the compressor so that the added load on the engine is compensated for by the ECM. Usually a/c request is straight to ECM (through HP cutout switch) and the ECM output (pin 43, ground output) goes through the relay. Fan request is via the ECM as well. Why do you need a trinary switch? If you want fans on when a/c compressor is on, then just wire the fans through another relay in series to the a/c compressor relay (a/c relay triggers fan relay).

Note: Your a/c on/off wire (from control panel) IS the a/c request wire.

https://lt1swap.com/99-02acwiring.gif

Last edited by Davidf; 09-21-2021 at 12:00 PM.
Davidf is offline   Reply With Quote
Old 09-21-2021, 10:43 PM   #3
chev-obsession
Senior Member
 
chev-obsession's Avatar
 
Join Date: Jul 2008
Location: kennewick, WA
Posts: 1,513
Re: AC compressor relay and Trinary switch wiring question

I’m using a trinary switch because it will turn the ac compressor on and off at set pressures plus turn the electric fan on.

I think i solved my question, let me know what you guys think.
Attached Images
 
__________________
1965 c/10 swb
1969 c/10 lwb
chev-obsession is offline   Reply With Quote
Old 09-24-2021, 03:29 PM   #4
Daaaanz67
Registered User
 
Join Date: Nov 2011
Location: Idaho
Posts: 857
Re: AC compressor relay and Trinary switch wiring question

That switch will help to keep the compressor from becoming a grenade and what he CO said.
Daaaanz67 is offline   Reply With Quote
Old 09-27-2021, 10:40 AM   #5
Davidf
Registered User
 
Join Date: Nov 2014
Location: Austin
Posts: 749
Re: AC compressor relay and Trinary switch wiring question

I still think a lot of functionality is missing. With this (above) wiring diagram, ECM control of the compressor is not present. Why not some form of:

A/C on/off from fan switch ->HP cutout on back of compressor ->ECM pin #17 (a/c request).

ECM pin #43 (ground output) -> compressor relay -> compressor

a/c LP cycling switch (or trinary switch, low side, I suppose) -> ECM pin #55

Condenser fans can be triggered by the compressor relay above so they come on whenever the a/c is on...good practice. Or, you can use fan 1 or 2 output from the ECM. Tell your tuner to trigger the fan output with the a/c request.

Last edited by Davidf; 09-27-2021 at 05:30 PM.
Davidf is offline   Reply With Quote
Old 09-27-2021, 05:11 PM   #6
kglowacky
Registered User
 
Join Date: Mar 2020
Location: The Woodlands,Tx
Posts: 588
Re: AC compressor relay and Trinary switch wiring question

going thru the same process of getting my ac working. when I got my harness back from the rebuilder he left a wire on it saying AC. I called and asked why he left it on there because I said no to ac on the build. He said they made a mistake just ignore it. Now I am wondering if he didn't do me a favor by leaving it. My question is is this wire connect to 12v or a ground or does it connect to the compressor and the compressor tell the ECM to increase rpms to handle the extra load. or connect to a relay terminal. Assume it is pin#17.
kglowacky is offline   Reply With Quote
Old 09-27-2021, 05:34 PM   #7
Davidf
Registered User
 
Join Date: Nov 2014
Location: Austin
Posts: 749
Re: AC compressor relay and Trinary switch wiring question

Quote:
Originally Posted by kglowacky View Post
going thru the same process of getting my ac working. when I got my harness back from the rebuilder he left a wire on it saying AC. I called and asked why he left it on there because I said no to ac on the build. He said they made a mistake just ignore it. Now I am wondering if he didn't do me a favor by leaving it. My question is is this wire connect to 12v or a ground or does it connect to the compressor and the compressor tell the ECM to increase rpms to handle the extra load. or connect to a relay terminal. Assume it is pin#17.
More than likely, he left you the a/c request line from/to pin #17 of the ECM. Most people wire the a/c request line together with the compressor wire (see above diagram by OP). The problem is that ECM is not controlling the compressor but rather the compressor request is controlling the ECM and telling it to increase idle due to the extra load. But, it really is too late at this point and you will feel dips in the idle speed.

On the other hand, if you let the ECM control the compressor, then the ECM anticipates the added load and compensates almost imperceptibly. And, the ECM can cut out the compressor as necessary such as during starting and full throttle, etc.

For ECM control of the compressor, ECM pin #43 must control the compressor. Pin #43 is a ground output and must only be used to control a relay.

Last edited by Davidf; 09-27-2021 at 05:42 PM.
Davidf is offline   Reply With Quote
Old 09-27-2021, 05:37 PM   #8
chev-obsession
Senior Member
 
chev-obsession's Avatar
 
Join Date: Jul 2008
Location: kennewick, WA
Posts: 1,513
Re: AC compressor relay and Trinary switch wiring question

Quote:
Originally Posted by kglowacky View Post
going thru the same process of getting my ac working. when I got my harness back from the rebuilder he left a wire on it saying AC. I called and asked why he left it on there because I said no to ac on the build. He said they made a mistake just ignore it. Now I am wondering if he didn't do me a favor by leaving it. My question is is this wire connect to 12v or a ground or does it connect to the compressor and the compressor tell the ECM to increase rpms to handle the extra load. or connect to a relay terminal. Assume it is pin#17.
I can’t answer the second half, I’m not an expert in the wiring harness stuff like some of the other guys on here are. If the wire he left in is green/white, it goes to the compressor, and not to the pcm (is the way I understand it) it’s more work to completely remove the wire and even more work to add it later if you changed your mind.

Did he leave the factory plug for the ac compressor on your harness?
__________________
1965 c/10 swb
1969 c/10 lwb
chev-obsession is offline   Reply With Quote
Old 09-28-2021, 02:16 AM   #9
Richard
Senior Member
 
Join Date: Dec 1999
Location: Southern California
Posts: 2,884
Re: AC compressor relay and Trinary switch wiring question

Would like control fans and AC as Davidf is pointing to. From my research this will not work with the e67 ecm.
__________________
Richard
1972 K10 Custom Deluxe SWB Fleetside
My build https://67-72chevytrucks.com/vboard/...d.php?t=800746
Richard is offline   Reply With Quote
Old 09-28-2021, 08:32 AM   #10
Rich84
Registered User
 
Rich84's Avatar
 
Join Date: Mar 2012
Location: Woodbury, Ct.
Posts: 1,692
Re: AC compressor relay and Trinary switch wiring question

I have a Vintage Air setup and use the trinary switch as they suggest. The fans only kick on when a set pressure is reached not just when you turn the AC on. I have never had any problems with idle. I have the AC request wire in my harness as well, but it is not being used.
Rich84 is offline   Reply With Quote
Old 10-13-2021, 11:54 PM   #11
chev-obsession
Senior Member
 
chev-obsession's Avatar
 
Join Date: Jul 2008
Location: kennewick, WA
Posts: 1,513
Re: AC compressor relay and Trinary switch wiring question

I am adding a low pressure cut out switch since the compressor is not cycling and freezing the evaporator. This is an updated diagram that I am asking Ls1nova71 to look at and verify. I moved the AC Request wire to terminal 87 on the compressor relay. I did that so the idle is bumped up only when the compressor clutch is on.
Attached Images
 
__________________
1965 c/10 swb
1969 c/10 lwb
chev-obsession is offline   Reply With Quote
Old 10-14-2021, 05:08 AM   #12
ls1nova71
Registered User
 
ls1nova71's Avatar
 
Join Date: Dec 2009
Location: Independence Mo
Posts: 4,119
Re: AC compressor relay and Trinary switch wiring question

That looks like it should work. The only thing I'm not positive about is the back feeding 12v to the AC request wire as I have never hooked one up that way, but I have heard it may bump the idle a bit, but again I have no first hand knowledge of it.
__________________
My '72 short bed build. http://www.ls1tech.com/forums/conver...6-0-4l80e.html

5.3 swap into my RUSTY '71 C10
http://ls1tech.com/forums/conversion...71-c-10-a.html
ls1nova71 is offline   Reply With Quote
Old 10-14-2021, 10:12 AM   #13
Davidf
Registered User
 
Join Date: Nov 2014
Location: Austin
Posts: 749
Cool Re: AC compressor relay and Trinary switch wiring question

I tried....

Do this, you don't need a trinary switch. Trigger the fan relay off of the compressor relay. Ignore PCM pins 33 and 11.

[IMG][/IMG]
Photo courtesy of lt1swap.com

Last edited by Davidf; 10-14-2021 at 02:17 PM.
Davidf is offline   Reply With Quote
Old 10-15-2021, 11:42 PM   #14
chev-obsession
Senior Member
 
chev-obsession's Avatar
 
Join Date: Jul 2008
Location: kennewick, WA
Posts: 1,513
Re: AC compressor relay and Trinary switch wiring question

Quote:
Originally Posted by ls1nova71 View Post
That looks like it should work. The only thing I'm not positive about is the back feeding 12v to the AC request wire as I have never hooked one up that way, but I have heard it may bump the idle a bit, but again I have no first hand knowledge of it.
Thank you
__________________
1965 c/10 swb
1969 c/10 lwb
chev-obsession is offline   Reply With Quote
Old 01-17-2022, 04:41 AM   #15
Richard
Senior Member
 
Join Date: Dec 1999
Location: Southern California
Posts: 2,884
Re: AC compressor relay and Trinary switch wiring question

Maybe late, I am still working on my project and still needing to address this. Fans on with compressor is not an option for me. Modern vehicles do not do that.
Found this informative thread from some time ago https://lateral-g.net/forums/showthread.php?t=40215 It is lengthy, so a long read. A lot of good info. From what I read there is zero reason to turn fans on with compressor.
Gives me hope that I can use the pwm fan control with its advantages from my e67 ecm.
Edit- maybe should have pointed out there is info on installing a stock gm pressure switch and connection to ecm. If you want stock type fan and a/c operation the thread is a good read if you can get though it.
__________________
Richard
1972 K10 Custom Deluxe SWB Fleetside
My build https://67-72chevytrucks.com/vboard/...d.php?t=800746

Last edited by Richard; 01-19-2022 at 02:26 AM.
Richard is offline   Reply With Quote
Old 01-20-2022, 04:25 PM   #16
Davidf
Registered User
 
Join Date: Nov 2014
Location: Austin
Posts: 749
Re: AC compressor relay and Trinary switch wiring question

Quote:
Originally Posted by Richard View Post
Fans on with compressor is not an option for me. Modern vehicles do not do that.
Hmm, I believe the condenser fan runs anytime the compressor is engaged on all of my BMW's. Albeit at a slow or high speed depending on need. But, it runs. Why would you NOT want the fan on when the compressor is engaged. The more the condenser is cooled, the more efficient the a/c system will be. The more efficient, the more fuel that is saved as the compressor will cycle off more often.
Davidf is offline   Reply With Quote
Old 01-24-2022, 02:47 AM   #17
Richard
Senior Member
 
Join Date: Dec 1999
Location: Southern California
Posts: 2,884
Re: AC compressor relay and Trinary switch wiring question

Quote:
Originally Posted by Davidf View Post
Hmm, I believe the condenser fan runs anytime the compressor is engaged on all of my BMW's. Albeit at a slow or high speed depending on need. But, it runs. Why would you NOT want the fan on when the compressor is engaged. The more the condenser is cooled, the more efficient the a/c system will be. The more efficient, the more fuel that is saved as the compressor will cycle off more often.
Newer cars are all about efficiency. There is no reason to run a fan when airflow is free at highway speeds. GM uses a pressure sensor to activate and deactivate fan for this reason. Not just to protect compressor. Have had two BMW's myself. Would bet they operate the same way. Unless you are using an 850+ watt fan in ideal conditions there is no way it will flow more cfm than running down the highway at speed with air being forced through the front of the car. So by running fan at speed you are most likely restricting airflow, not increasing it.
Older vehicles such as the 67-72 trucks use a clutch on the fan to disengage it when not needed. It is regulated by heat. The electric sensors are just taking this a step further. There was nothing to fully engage the fan when a/c was turned on and the ac worked fine.
__________________
Richard
1972 K10 Custom Deluxe SWB Fleetside
My build https://67-72chevytrucks.com/vboard/...d.php?t=800746
Richard is offline   Reply With Quote
Reply

Bookmarks


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 01:01 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com