How to have A/C turn on engine fan ???

[lts70]

I just got done installing my Vintage air system last night and decided I want to hook my engine cooling fan up to the A/C system. I want my fan to come on when I turn on my A/C. Right now I have my fan running off of an adjustable thermostat then through a relay. How are you guys accomplishing this in your trucks? I would think I could run a wire from the fan switch on the A/C control unit (original) to the relay so that when I turn on the A/C blower motor it would activate the engine cooling fan. Any advice and even wire routing would be appreciated.

[storm9c1]

I would patch the fan relay into the A/C request signal from the dash. Basically you can pull that signal from the power feed to the clutch (or the low pressure/cycling switch if that comes first in the chain). That feed will be under the hood. If you take it from the clutch signal (after the cycling switch) the fan will cycle with the clutch itself and I wouldn't recommend that.

[lts70]

So you are saying to tap into one of these termanals on the controler blower knob? Or the wire coming off of the compressor? The wire coming off of the compressor goes to an inline binary switch/sensor in the ac line itself.

[storm9c1]

I'm not sure what you mean about the blower, I mean, the blower can be used with or without A/C (ie: for heat). So there has to be another switch that turns on when you select the A/C mode. When A/C mode is selected, it will send a signal to the compressor. If you can tap into that switch at the dash that would be fine. However, what I would do is simply use the signal that you already have under the hood that already comes from the dash that tells the compressor to turn on.

The question I have is where does this wire go after it leaves the dash? Does it go straight to the compressor (and the cycling switch in the A/C line may cycle the ground) or does it go to the cycling switch. Did your Vintage Air system come with a schematic for the wiring that controls the compressor? That will tell me everything I need to know.

[lts70]

Thant would be great! See attached file.

[mrein3]

If its a stock system, the clutch doesn't cycle.

If that is what you got, just run a wire from the green wire on the AC power connector on the compressor on to the control side of your fan relay. When the compressor kicks on, it will energize the relay and you're good to go.

[Sinister]

Vintage Air has an optional Trinary switch that I believe is used to run an electric fan.

[lts70]

I had already completeled my system with a bianary switch before I learned about the trinary switch. Looking for options of how to do this with the system I have.

[lts70]

So correct me if I am wrong, what I understand is if I tap in to the wire that goes from my compressor to my binary switch and run that wire to the control side of my fan relay I should be good to go? I will try posting a picture with a white arrow pointing to the wire I am talking about. If this is the correct wire to tap into I will be able to just cut off the connector at the binary switch to that wire and crimp a new spade connector with both the compressor wire and fan relay wire nice and clean & simple.

[lts70]

I am going to try doing this today. Just wanted to check with you guys to make sure the wire pictured above is the right one to tap into. Thanks

[bigsnookmaster]

I used the trinary switch and had no problems.

[lts70]

So I think I understand now. The wire coming from under my dash goes to my binary switch then out out the binary switch to my compressor. So if I tap into to that signal wire when I turn on my ac it will turn my fan on as well. when I tested this wire with my volt meter it showed around 9 volts when ac was on and 0 when off. the

My problem now is that my trigger to my fan relays is negative not positive. I don't know how to make this wire trigger my relay as it is positive. Any help on how to do this would be great. I will post my fan wiring schematic.

[Zeke]

You could add another relay as a contol which would ground out when activated.

[lts70]

Thanks for all of the help guys. I will be sure to leave rep points! I got it done last night and it works great. I tapped into my compressor activation wire coming form the unit under the dash, that way it is before the binary switch and my fan will not turn off if my binary switch trips. I then ran the split into a relay at the trigger wire, and converted the positive to ground.

[storm9c1]

Sorry that I didn't get back to you sooner...I was tied up all weekend and didn't even get on the computer. But what you did is exactly what I was trying to explain in my original reply. Glad it worked!

[lts70]

I just got a call back from vintage air (left them a message last week asking what they suggest) They say I need to switch my system to a trinary switch system as my fans life will be greatly diminished by having it run while on the freeway. With there trinary switch the fan will only run when the system needs the fan (at certain head pressure settings) and not all the time like the way I have it set up. The new switch will cost $40 and can be installed without loosing my Freon.


What do you guys think, Run it the way I have it or go with the trinary? Will it realy mess my fan up?

[Sinister]

Run the Trinary.

[jorgensensc]

trinary

[storm9c1]

You know what, they are right. Not only will it decrease the fan life, but it will decrease air flow through the rad at highway speeds due to the conflict between the fans trying to move air while the air is moving faster than the fans can move it.

I know modern cars are setup to turn off the fans at highway speeds. I didn't think of this when you made your original post.

Get the trinary switch. That sounds like the right thing to do. After you do that, I would wire up a light or LED on your dash to the fan motor to make sure they are really turning off at highway speed.

[lts70]

Well I just ordered the trinary switch from vintage air. Good thing switch them out is easy as they are on a shrader valve.