DIY dual fan mod

[— Agent☣Orange —]

This mod has been around a little while and involves jumping two wires at the ECU to make both, the AC and cooling fans come on concurrently. Either event (cooling or air conditioner) will trigger both fans to come on instead of just one.

There are two ways to do this mod. The first way is the simplest and just involves jumping two wires. The other way is to connect a switch to the same two wires. A switch obviously allows the user to decide whether to turn dual-fan mod on or off.

This could be handy to manually regulate electrical draw on the system or for adapting to changes in climate (summer-winter) and as an excuse to buy another switch to play with because dudes love switches.

With the right parts, there will be no damage to the wiring and the mod can be undone at will but why would you do that?

[— Agent☣Orange —]

The right parts:

Package of quick splice connectors for 22-18 gauge wire. These are great because unlike the vampire clips of the past, these allow a wire to be unplugged and plugged back in like a poor-man's switch and also because you might decide to install a switch later and these make it easy.



Switch and wire (*optional) You have many choices here. If you want a little toggle at the splice or maybe by the hood release or tucked away underneath, get a micro switch. If you want something fancier to mount in the dash or center console, there are too many cool switches to show here so I'll just picture the one I used. The wire can be a simple, foot or so of 18 gauge speaker wire (depending where you place your switch).

[— Agent☣Orange —]

The work:

*Make sure you have researched the location and pinout of your ECU before anything else. Print a copy if you have to. On my 2002, I used this diagram of the smallest of the three plugs connected to the ECU which is located above the clutch pedal in my car.

Yours may be under the passenger footwell or behind the passenger seat and the wires may be a different color but the mod is the same. I don't know where yours is or which wires to splice so do your own research.

Start by making your wiring on your workbench which is much easier than trying to do it upside down in the car. If you're going to make a simple jumper, make a short, 1-2 inch wire with two red connectors from the package on each end.

If you're going to install a switch, cut a length of a wire pair (ie thin speaker wire) comensurate with where you're going to place the switch and then crimp a pair of red connectors from the package to one end. Leave the other end untouched so you can route it to your switch later.

For 2001-2005, if you can contort your back, great, kneel down next to your open car door and try. If not, take out the driver seat, put a pillow in the well and lay on your back with your legs over the parcel shelf and a flashlight in your mouth.

Make sure you have the connectors, the wire you just made, small flat head screw driver (to unplug the connector from the ECU) and pliers (to crimp the connectors) ready by your ass so you can easily reach down and get them by feel as you need them.

You won't be able to move your elbows too much reaching way up to the ECU and if you put all the stuff on your chest, they'll just roll off to your sides and you won't be able to reach up by your arm pits to get them.

Optionally, you may just unplug the connector to bring it lower and make it easier to work with. With 2001-2005s (again verify your research), it is the smallest connector of the three and luckily, it is the bottom-most. You may depress the locking tab with your finger or a short, flat head screwdriver and wiggle it free.



This is the pinout of that connector, (remember, it's the smallest of the three) showing the two affected wires circled in red (red with yellow stripe is the cooling fan and blue with white stripe is the AC fan) *Note: "L" in the diagram means blue so L/W means blue wire with white stripe.


Separate the two wires from the bunch and crimp on the quick connectors.


If you're just going to jump the two wires, you should have made a 1-2 inch jumper with the red connectors crimped on each end to just plug in and done.

If you're going to run a switch, you should have made a length of wire determined by the location of your switch, again, with the red connectors crimped on each end.

Either way, just plug them in. (Now you can see why these new connectors are so great. You do most of the work on the bench and then just plug them in). Obviously, this photo only illustrates how they connect as I haven't done the work on the bench yet.


Okay, now it's for real. I've decided to use a switch for my install so I've connected the wire and gave myself enough length to reach my switch including a little extra.


This is where everyone's going to be different. I chose this particular switch and this particular location for my install but you make decide on a completely different switch and location altogether of course.

[— Agent☣Orange —]

Now time to test:

Start your car and immediately use the AC (before the car has warmed up). Both fans should come on. Shut off the AC and then idle or drive your car until it fully warms up which will trigger the cooling fan. Again, both fans should now come on. If you installed a switch, verify that you can turn on and shut off dual-fan mode in each of those tests.

Project notes: I'm still working on switch labels so I mine can say "Dual Fan, on-off" or something. Thanks to Tom at Fast Forward Superchargers for the 2001 ECU pinout.


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[jnshk]

Nice write-up!

[I<3flippyheadlights]

You sir are a genius.

[— Agent☣Orange —]

Awesome! It's been up for a while and nobody had bothered to read it, haha.

[I<3flippyheadlights]

I'm doing this also, just in a different way. Its what I call, "Rip out the not working AC" method

[— Phatmiata —]

that looks like an OEM install, very nice write up!

[Tristan75]

Fantastic write up Yellow!

[— Agent☣Orange —]

Thanks Tristan! Have you done it yet? I know you got that Megasquirt and didn't know if that is a setting you can just switch on instead of wiring.

[curvingedge]

Not to sound sarcastic, what would be the point of doing this mod? Looks interesting just to keep the rad cooler...

[curvingedge]

Not to sound sarcastic, what would be the point of doing this mod? Looks interesting just to keep the rad cooler...

I made a noob mistake. Just did this mod and boy does my AC blow colder while sitting still or eating lunch! Thanks for the walk through yellow

[— Agent☣Orange —]

Right on! Another cool(er) customer.

[silvermazda]

hm...anyone ever measured the amp load on the fans? I was thinking it was bad to suddenly want an extra 10+ amps. I did this mod a different way.
I hooked up the T-splice and eventually manually ground it to a switch. AKA AC fan on demand (gotta find a 190-200F circuit breaker/thermal switch).
And second hooked up the non func. AC or jumping the pressure switch so I can actuate the AC fan when I press my AC switch. So I have 2 ways right now.

why?
Because I'm hoping keeping the engine in a constant temp will give better mileage/performance (I've seen it richen when hot).
Second, constant temp at stop lights, periods of slow movement/hill climbing.