Electric fans & Vintage Air

[Rich84]

I have a 2006 LQ4 with electric fans that are activated by the PCM. They are wired with a factory harness and relays from an Escalade. Since fans are enabled in the pcm, if I connect the A/C request wire from the harness to a 12v source when the A/C is on will the fans function as they should from the factory or do i need a trinary switch?
Where exactly should the request wire be hooked up?

[MDPotter]

I would give Vintage Air a call. They have a wiring diagram for this exact situation and can help. We ended up using the trinary switch.

[Gunnin4ya]

I used the Trinary and it is working good. Very easy to set up for fans.

[ls1nova71]

Originally Posted by Rich84

I have a 2006 LQ4 with electric fans that are activated by the PCM. They are wired with a factory harness and relays from an Escalade. Since fans are enabled in the pcm, if I connect the A/C request wire from the harness to a 12v source when the A/C is on will the fans function as they should from the factory or do i need a trinary switch?
Where exactly should the request wire be hooked up?

What harness/PCM are you using? Because a 2006 harness doesn't have an A/C request wire, they are the serial data type.

[Rich84]

Typo. It's a 2005.

[ls1nova71]

2005 doesn't have one either unless the harness/PCM is out of a van, in which case it wouldn't have electric fans. Is it a factory harness or aftermarket? It's most likely going to be easiest to just use a trinary switch set to trigger the ground on the high speed fan relay.

[Rich84]

It's a harness made by Fuel Injection Connection. The pcm and engine are from an Isuzu NPR. I am using a stock fan harness and relay setup. So I would splice the wire from the trinary switch into which fan ground 1 or 2. I believe the way they function now is both operate at low speed when fan1 is triggered. Both operate at high speed when fan 2 is triggered. It would be simple if all I had to do was hook up the A/C request and the PCM would operate the fans.

[ls1nova71]

Just for grins, I looked up an A/C schematic for an Isuzu NPR, thinking it was going to be like a van, but it's more like a pickup, with the 3 wire pressure sensor. I think without any signal from that sensor it will either not turn the fans on, or it will possibly default them to "on" as a precautionary measure. You might just try it, but I'm not sure it will work since I didn't notice a 12v A/C request in the diagram, so not sure why you have a wire there. Pretty sure its a serial data signal sent to the A/C modules that turns it on in them just like the trucks. It could be they put one in the slot that the older 2002 and back trucks had?

[Rich84]

Thanks for checking. I guess I'll order the Vintage Air and get the trinary just in case. With the switch I should splice it into the #2 trigger I presume. I have never actually seen my fans run on high before except for when I tested them.

[ls1nova71]

Yes, I would use the high speed signal so the condenser gets the most cooling it can get.

[Rich84]

Question: Can I just supply 12v to the A/C wire and see what happens? If the fans don't turn on I'll get the trinary switch. The kit should arrive in a couple of weeks.

[ls1nova71]

Originally Posted by Rich84

Question: Can I just supply 12v to the A/C wire and see what happens? If the fans don't turn on I'll get the trinary switch. The kit should arrive in a couple of weeks.

It's hard to say without knowing exactly what that wire is hooked to in the PCM. But I doubt it will work since the schematic I looked at for your engine didnt show one.

[Rich84]

I put 12V on the A/C request wire and nothing happened. I will be ordering the Trinary switch.
With a factory type 2 fan 2 speed setup do I need to hook the trinary switch to both fan grounds or does the high speed signal trigger both automatically?
Will it trigger an CEL?

[Rich84]

Finally had a hot day. AC works great. I tied the trinary to the high speed trigger wire. One fan runs at high speed. I’m not sure what will happen if the engine reaches the temperature to trigger the low speed. I’m not sure it ever will as it seems to keep it pretty cool with the one fan.

[First c10]

If low speed is one fan (fan1)and high speed is the addition of the second fan(fan2) then the trinary switch will call for high speed fan(fan2) to be on as long as ac is on. If the engine reached the low temp set point in the pcm then fan1 will come on and both fans will be on.
I didn’t use a trinary switch I just added a relay so when I turn on the ac it turns on high speed fan. I used the original ac system binary switch for compressor protection only.

[First c10]

Other post about this
http://67-72chevytrucks.com/vboard/s...=781489&page=2
Or
http://67-72chevytrucks.com/vboard/s...d.php?t=776599

[ls1nova71]

Originally Posted by Rich84

Finally had a hot day. AC works great. I tied the trinary to the high speed trigger wire. One fan runs at high speed. I’m not sure what will happen if the engine reaches the temperature to trigger the low speed. I’m not sure it ever will as it seems to keep it pretty cool with the one fan.

If you're using a 3 relay set up, and tie the trinary switch to the high side, it will only turn on one fan like you're seeing, but it should be alright. If the engine reaches the point it needs the low fans to come on, then both fans will run on high. It will be perfectly fine running this way as long as one fan is enough to keep the condenser cool, however most of the time in the summer when it's hot enough to need A/C the low fan will already be on so both fans will come on high when the trinary switch commands the fans on which should be sufficient to cool the condenser.

Originally Posted by First c10

If low speed is one fan (fan1)and high speed is the addition of the second fan(fan2) then the trinary switch will call for high speed fan(fan2) to be on as long as ac is on. If the engine reached the low temp set point in the pcm then fan1 will come on and both fans will be on.
I didn’t use a trinary switch I just added a relay so when I turn on the ac it turns on high speed fan. I used the original ac system binary switch for compressor protection only.

A trinary switch will not keep the fans on the entire time the A/C is on, it only turns the fans on when the head pressure is high enough to require it. So for example, at highway speeds the condenser is getting as much air as it will ever get so the head pressure will be low and the fans wont be running all the time. Similar to the way the PCM shuts the fans off above a set speed, somewhere around 40mph. It will add life to the fans not running all the time, and some have speculated that fans running at highway speeds can actually hinder air flow, although I'm not real sure about that.

[First c10]

Originally Posted by ls1nova71

If you're using a 3 relay set up, and tie the trinary switch to the high side, it will only turn on one fan like you're seeing, but it should be alright. If the engine reaches the point it needs the low fans to come on, then both fans will run on high. It will be perfectly fine running this way as long as one fan is enough to keep the condenser cool, however most of the time in the summer when it's hot enough to need A/C the low fan will already be on so both fans will come on high when the trinary switch commands the fans on which should be sufficient to cool the condenser.


A trinary switch will not keep the fans on the entire time the A/C is on, it only turns the fans on when the head pressure is high enough to require it. So for example, at highway speeds the condenser is getting as much air as it will ever get so the head pressure will be low and the fans wont be running all the time. Similar to the way the PCM shuts the fans off above a set speed, somewhere around 40mph. It will add life to the fans not running all the time, and some have speculated that fans running at highway speeds can actually hinder air flow, although I'm not real sure about that.

If using the 3 relay system you might have to turn off the MIL in the tune for low or high fan as on my setup it through a code and light since the PCM was getting a ground when AC was on but other than that LS1 is correct.

I do believe the trinary switch on a r134a system will come on most of the time due to the set point for the fans. Do you know what the set point is? if I remember right it is around the high end of the operating pressure of a r134a system. Since I tried to wire in the stock pressure switch but needed the costly canbus portion I just wired in the relay. Now maybe I need to rethink and remove the stock sensor and binary for the trinary.

[Rich84]

I believe that the trinary switch closes when the high side pressure reaches 240. So far I have not had a check engine light with its operation.

[First c10]

Originally Posted by Rich84

I believe that the trinary switch closes when the high side pressure reaches 240. So far I have not had a check engine light with its operation.

At 240 I think the fan will come on and stay on as long as the compressor is on right?
Do you have the trinary set to control high speed or low speed?

[Rich84]

The fan will stay on as long as the pressure is above 240. I have it tied into the #2 fan trigger wire from the computer. #2 fan trigger is high speed. So far I have not seen the temperature increase enough to force both fans on. I'm not sure it ever will because that fan on high keeps the engine a little cooler then it is normally.

[ls1nova71]

Originally Posted by First c10

At 240 I think the fan will come on and stay on as long as the compressor is on right?

Not necessarily, it depends on many variables. Sure, idling on a hot day, the fans probably will not shut off, but on cooler days they might, also, once moving, and air is naturally forced across the condenser then they will shut off.