Adding trinary switch signal to fan relay setup
Thread Starter
On The Tree
Joined: Sep 2010
Posts: 197
Likes: 1
From: Phoenix, AZ
Adding trinary switch signal to fan relay setup So I have a (3) relay high/low fan switch module. It receives two temperature signals from the PCM, one for low speed and the other for high speed.
These are ground signals as I understand it.
I have an Oldairproducts AC system and a trinary switch which outputs a ground signal at a specific pressure.
Is it OK to just "tee" that trinary wire into the high speed signal wire from the PCM?
Thanks!
Joe
These are ground signals as I understand it.
I have an Oldairproducts AC system and a trinary switch which outputs a ground signal at a specific pressure.
Is it OK to just "tee" that trinary wire into the high speed signal wire from the PCM?
Thanks!
Joe
If you've got access to a way to turn off the trouble codes then you can just Tee it like you mentioned. When you Tee off the PCM with an alternate ground you will get a trouble code on the fan for a non commanded ground.
The last build I did I ended up using a very small relay off the PCM fan circuit to kick on the larger fan relay. This isolates the PCM command wire from ever seeing the trinary switch grounding the system.
The last build I did I ended up using a very small relay off the PCM fan circuit to kick on the larger fan relay. This isolates the PCM command wire from ever seeing the trinary switch grounding the system.
Perhaps you didn't have the diode facing the right way? I used this approach to get a working alternator light on my conversion without sending some 'errant' 12V (+/-) to the ECM. If the diode is facing the right way, the wire you're tied to (the one that the ECM makes a 'ground' to signal the fan relay) will never know anything is connected to it.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo I'd put it in the trinary wire before the tee - so there's no way the existing ecm/ground/fan relay wire "sees" anything from the trinary ground. I'm assuming you're running a separate circuit/relay to fire the fan(s) from the A/C.
Thread Starter
On The Tree
Joined: Sep 2010
Posts: 197
Likes: 1
From: Phoenix, AZ
If it's in the trinary wire, won't the pcm wire wire see the ground then? Thought if the diode was on the pcm wire it will block the trinary signal from traveling upstream to the computer.
I must be thinking of this wrong?
I must be thinking of this wrong?
TECH Addict
Joined: Oct 2016
Posts: 2,513
Likes: 480
From: PDX-OR-USA
diodes have a threshold and current breakdown voltage, in other words they will leak enough current for the ECU to spot in some cases.. I always relay isolate ECU circuits, ECU's cost too much..
As pdx points out, be sure you size the diode correctly.
joz -- you're not thinking of it wrong; we're imagining different circuits. I don't see why your schematic wouldn't work. What happens if the trinary switch sees a ground from the ecm when the ecm fires off the fans? Is that a problem? If so - another diode in the trinary wire I suppose.
joz -- you're not thinking of it wrong; we're imagining different circuits. I don't see why your schematic wouldn't work. What happens if the trinary switch sees a ground from the ecm when the ecm fires off the fans? Is that a problem? If so - another diode in the trinary wire I suppose.
Thread Starter
On The Tree
Joined: Sep 2010
Posts: 197
Likes: 1
From: Phoenix, AZ
I think I can just use a fourth relay triggered by trinary ground signal and tee output side into the fan wire?
Obviously, my sketch doesn't show the low speed part of the existing relay setup.....
This should physically isolate the trinary side from the pcm temperature controlled side, correct?
Obviously, my sketch doesn't show the low speed part of the existing relay setup.....
This should physically isolate the trinary side from the pcm temperature controlled side, correct?
TECH Addict
Joined: Oct 2016
Posts: 2,513
Likes: 480
From: PDX-OR-USA
This is how I just did my Honda, I wanted to have the fan cut in lower... So in my case the AC switch is a temperature switch that turns the fan on at 185 instead of 238.. (Yes really Honda doesn't think you need to cool the engine till it hits 238.. )<br/>
Thread Starter
On The Tree
Joined: Sep 2010
Posts: 197
Likes: 1
From: Phoenix, AZ
Ok, i see what you are saying there. Think my second sketch is the same thing?
My relay set-up uses three relays to get high and low speeds. Thinks it's a series/parallel thing to get high and low?
I think just the added stand alone relay for the trinary hooked to the fan input lead should give me 12V and "high" speed, no?
Now what happens when the trinary sends 12V to the fans and the pcm sends high temp signal together?
Pdx, I also had my harness guy edit my fan temps to be lower (think I'm 195 & 110 or 115, it's been a while...).
My relay set-up uses three relays to get high and low speeds. Thinks it's a series/parallel thing to get high and low?
I think just the added stand alone relay for the trinary hooked to the fan input lead should give me 12V and "high" speed, no?
Now what happens when the trinary sends 12V to the fans and the pcm sends high temp signal together?
Pdx, I also had my harness guy edit my fan temps to be lower (think I'm 195 & 110 or 115, it's been a while...).
TECH Addict
Joined: Oct 2016
Posts: 2,513
Likes: 480
From: PDX-OR-USA
Since there is no difference in potential load between the switching half of each relay, the PCM or the AC will always have authority to hold the fan ON. (Kinda a backup)
The reason I used 2 relays , was because my computer just would not deal with more Relay loads on the trigger wire, so I was stuck.. Had to use the two relays.. (Like yours mine has a low and high but I'm only showing the high circuit here... ) and the PCM relay is the factory relay on mine.. The other one is one I added...
The reason I used 2 relays , was because my computer just would not deal with more Relay loads on the trigger wire, so I was stuck.. Had to use the two relays.. (Like yours mine has a low and high but I'm only showing the high circuit here... ) and the PCM relay is the factory relay on mine.. The other one is one I added...