By popular request, a cooling fan switch DIY....

IMPORTANT -Normally a DIY would show the wires and the switch mounting, but if you need that depth of instructions, I stongly suggest that you don't attempt it, this mod has the potential to damage your ECU and/or fry your wiring harness!

First a description of the fan system - there are two fans (A & B) controlled by three relays, wired in two circuits (1 & 2). The two sets of relays get switched power from the ECU power circuit and the computer grounds the relays to activate.

When relay 1 closes, A & B fans run at half power.
When relay 2 closes, fan B runs, full speed.
When both relays close, both fans run full speed.

If you want "switch control" for your fans, I would suggest your switch grounds relay 1, (red/green wire on "Cooling Fan Relay #1") to run both fans, on slow speed. This could be left on without too much wear on the battery or fans, doesn't interfere with the stock ECU speed control, and only requires a simple switch and a ground connection.

Activating just relay 2 would run a fan at high speed, and you would lose the stock "two fans, slow" setting.

Activating both relays would need diodes inline to maintain the stock ECU control, as well as being a large current drain.

S

 

Sweet! Once I locate the relays I'd love to try this

 

U beat Jeff to it.. he told me he wanted to post a DIY in the next few days

 

Now we need DIY for a fan controller that uses as an input the factory ECT sensor.

 

It's called re-flash.. I know RE-Amiya does this in their reflash

 

RB also doing it. But not for 2005 cars yet. So in the meantime we need something. Actually I've done some research and found a simple and cheap solution. I'll try it this weekend and if it is a success I'll post DIY.

 

SC-ed, what are you aiming for?

I'm imagining a comparitor reading the coolant sensor. We need to figure out what voltage to trigger at, and then we can use a resistor divider to set the trigger temp. I bet we can find a comparitor with a big enough output current to be able to drive the relays directly.

We should only need:

Voltage regulator
Comparitor
Two resistors

We do need to come up with an easy way to hook into the four wires we need though.

 

Wouldn't this work pretty well?

Painless Wiring Electric Fan Relay Kit. 60 bucks from summit. 185F on/170F off.

yay/nay?

 

Yeah, it would work, but you have to mount the sensor somehow. That's what using the stock sensor gets you away from.

 

Yeah but isn't that exactly what scotts doing as well? You have to splice into the coolant hose anyway for his product.

 

I'd rather cut into the coolant hose than the ECU wiring harness. If you induce feedback you could blow the ECU...and that would be a lot more expensive than the $150 for the mod

 

Something like THIS for $5.

Or replicate the Scott mode for about $20.

 

Scott's system has to hook to the ECU too- the fan output drives the relays and so does his system, so something could go wrong there as well.

Clearly what we are talking about here isn't for just anyone as was stated in the first post. If Scott's system is easer / faster / safer for you then by all means get it.

The EE in me has to chuckle at "inducing feedback" into the ECU. Yes, you could hook it up really wrong and damage the ECU, but that's true of any system. The design we are discussing would have zero chance of hurting the ECU when hooked up correctly. Extend any argument like that far enough and you shouldn't get in your car because "there's a chance I'll get in to a fatal accident."

SC-ed, that's exactly what I was talking about. Few resistors, op-amp or comparitor.

That design has a flaw when used in a car though- the trigger voltage varies with the car's voltage. You need to stablize the reference that is created by R3/R4. You can do this with a voltage regulator or a zener diode.

We should also design some hysteresis into our circuit so that the fans turn on at X degrees and off at X-Y degrees. That design you have is a bang-bang controller and might click on and off pretty quick as the temperature hovers near the trigger point. You do this with a feedback resistor on the output to the trigger value so the trigger alue gets lowered once the thing turns on.

 

Yah, I know, this was just an idea, needs some work.
Hey, dsm you are the EE. My electronics knowledge is a little basic. I understand what you are talking about but I don't know how exactly has to be accomplished.
Lets do it, man. If you design it I'll be the genuine pig.
What do you say?

 

Or better this one:

http://www.customstreetdesigns.com/4062-FAN-PWM.htm

Will use factory ECT sensor, program any temp range and with the secondary fan control output you have Scott's mod. Also using the A/C input you can wire a switch and force the fans on 100% if you need.
Sounds good - full fan control for $60.

 

^^ hmm interesting, thanks for that link!

 

bump

 

thread highjack--but for the EE--how could we rig a switch to keep the fuel pump in the fast mode for track days?
olddragger

 

how well does this work? does it cool alot?

 

I see the point and yea it might keep your car cooler but a switch?? i know id forget to switch it on when im doing my daily driving. i think ill just leave my car cool itself

 

i'm working on a module to set fans on earlier... since mazsport is well i don't know where.... this won't be expensive and for those of you that don't want to buy a reflash or any other stuff that cost too.. much.... also i'm working on a module that activates the highspeed part of the fuel pump unit according to boost or throttle position... and these will work for all mazdas

 

I know this is a really old thread, but can anyone tell me why I have three yes 3 fan control relays? 2black and 1 blue? Help... thanx

 

Stealth said in the first post that there are 3 relays for both a&b fans.
I dont know how all 3 work together but what I dont know is if you want to turn on your fans with a switch
just ground a switch and run the grounded wire to the red/green wire on "Cooling Fan Relay #1"
the fans will only run at half speed and only when the car is on.

 

Ok, although I'm pretty damn sure he only wrote 2 but, doesn't matter. So it says what relay 1 and 2 do, what does the third relay do? It's not mentioned above. On the Haltech I have 4 pwm outputs so I was thinking that I would ground the first relay to work both fans at half speed for a certain lower temperature range with pwm1(which grounds) and pwm2 to ground the second relay at another higher temperature range while the first relay is still grounded to make them work at full speed. I'm confused with the 3rd relay and what it's operation is. Does anybody know what color the wire is for the second relay that has to be grounded? Thank you very much!

 

Great Posts, Great Data

Taking the data above, and being too lazy to dig into the harness, I pulled the relay, used a volt meter to find the control side of the relay (the one without 12 volts on it), and soldered a wire (stranded, 20 ga'ish) to that leg of the relay, with the joint in the middle of the pin so as to not mess with the connector, and then ran the wire to one of the bolts that holds the fuse/relay box to the car for a ground. I chose the bolt in the back, because it let me easily run the wire out the same path that the two big power cables came in on. Now, if the car is on, the fans are on low. Car is off, fans shut off in about 10 seconds.

Pending testing, I will likely run this way in the summer, and when it cools down here in Florida, I will probably put in a switch as opposed to cutting the wire. Needless to say, the switch will be on for track days.

Note, on the 04, relay 2 is only active if relay 1 is already on.

Solder instructions.
The relay has 4 tabs that come out of it. Two are copper, and larger than the other two. These are the ones that are controlled. The other two, the smaller ones, are the ones that control. The one you want to solder the wire to is the one towards the front of the car when the relay is installed. The reason I put the wire in the middle, was to make it easy to put in the connector. The reason for stranded wire was that I could make it flat, again to make it easy on the connector. I also filed it smooth when I was done to make it easier to install.

I will update if it works as planned, or if the whole thing catches fire.

/edit/ It is working wonderfully, car has not caught fire /edit/

Mike