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switching from clutch to electric fan for the first time, have a few questions
rx7 with a turbo Swap. I have a microteach LT9C ECU. I've been wanting to convert to an electric fan because I think it would perform better compared to what I have now (my fan shroud isn't sealing against the radiator at all and it has a cut in it, also I think the clutch is going out.) plus I plan on adding a pusher fan and splice that into the AC pressure switch so I thought I'd get it all done at once.
I have the wiring for the main fan pretty much set up in my head, and I found this article that says that gives the general idea of how to set it up: How To Properly Install An Electric Fan (aaroncake.net)
only issue is, I want to use my ECU to control the fan, or at least that is what I'd like to do, since it already has a signal from the thermostat and aux outputs that aren't being used for anything anymore (they were previously used for the idle air control valve for the AC but it keeps making the engine bounce at idle and I could never figure it out so i'm doing away with it.)
I've gotten into tweaking and tuning the ECU but I wouldn't even know where to begin on this, so any advice on this would be greatly appreciated. also wondering if there is any way to adjust fan speed or if its going to be just all the way on or off.
one last issue to cap it off, the fan im going to be using to replace the clutch fan was being used on the previous owners FC but Im not sure what the current draw is so ill post some pictures of it, or if someone could give me a way to find out how much it draws that would be appreciated too!
The fan looks like it has only two pins, so it is likely a simple on/off fan. Current draw isn't easy to tell unless you know what model of fan it is or where it came from, but here's what I'd do:
- Get a quality relay. I'm using one rated for 70A.
- Get a 60A fuse and carrier.
- Run relatively thick wire for it. I'm using 10GA.
The relay works like a switch. Two terminals are a coil, and two are a switch that is normally opened. There are some five pin relays that have a normally opened and normally closed pin. You'll want to use it in the NO arrangement, otherwise the fan runs constantly while cold and then turns off when hot.
Basically you'll use an output from the Microtech to energize one side of the coil with 12V at the chosen temperature. Then the other side connects to GND. This causes an electromagnet to close the circuit on the other two terminals, which closes the circuit for the fan. In this way a small circuit (ECU switch) can power a big fan without burning up the ECU.
You should have one wire that comes from the fan GND pin to the chassis. Then the positive wire comes from battery positive, through a fuse (to protect the wiring in case of short), then to one of the switch terminals on the relay. Then the other switch terminal on the relay will go to the fan 12V pin.
One wire comes from an ECU output pin to one side of the coil. The other side of the coil goes to GND.
There will be a diagram on one side of the relay that tells you which pin is which.
Then presumably you just need to program the Microtech to power that output pin at the appropriate temp, so you'll need to check the documentation to see how that works as I don't have a Microtech.
The fan looks like it has only two pins, so it is likely a simple on/off fan. Current draw isn't easy to tell unless you know what model of fan it is or where it came from, but here's what I'd do:
- Get a quality relay. I'm using one rated for 70A.
- Get a 60A fuse and carrier.
- Run relatively thick wire for it. I'm using 10GA.
The relay works like a switch. Two terminals are a coil, and two are a switch that is normally opened. There are some five pin relays that have a normally opened and normally closed pin. You'll want to use it in the NO arrangement, otherwise the fan runs constantly while cold and then turns off when hot.
Basically you'll use an output from the Microtech to energize one side of the coil with 12V at the chosen temperature. Then the other side connects to GND. This causes an electromagnet to close the circuit on the other two terminals, which closes the circuit for the fan. In this way a small circuit (ECU switch) can power a big fan without burning up the ECU.
You should have one wire that comes from the fan GND pin to the chassis. Then the positive wire comes from battery positive, through a fuse (to protect the wiring in case of short), then to one of the switch terminals on the relay. Then the other switch terminal on the relay will go to the fan 12V pin.
One wire comes from an ECU output pin to one side of the coil. The other side of the coil goes to GND.
There will be a diagram on one side of the relay that tells you which pin is which.
Then presumably you just need to program the Microtech to power that output pin at the appropriate temp, so you'll need to check the documentation to see how that works as I don't have a Microtech.
would a one speed fan work for street use? and if I wanted a lower speed couldn't I use a resistor to lower the amperage?
would a one speed fan work for street use? and if I wanted a lower speed couldn't I use a resistor to lower the amperage?
One speed is fine. Mine is a two speed and I'm currently only using the low-speed. Never had an issue. Make sure to keep an eye on temps for the first few drives though, just in case.
I'm not an electrical engineer, but I believe a resistor reduces the voltage. Not the current. Regardless, I'm not sure why you'd want a lower speed? It would have to be ridiculously noisy or something to warrant lowering the speed.
One speed is fine. Mine is a two speed and I'm currently only using the low-speed. Never had an issue. Make sure to keep an eye on temps for the first few drives though, just in case.
I'm not an electrical engineer, but I believe a resistor reduces the voltage. Not the current. Regardless, I'm not sure why you'd want a lower speed? It would have to be ridiculously noisy or something to warrant lowering the speed.
Voltage / resistance X current
that's the formula to calculate voltage, amperage, and/or resistance. if resistance goes up, current goes down. Voltage is simply the charge, now how fast its going through the wire, that's what current is if that makes sense so theoretically it would work.
not sure how exactly the microteach tells the fan to switch on or off but when I look at my temps when its hooked up to my computer it likes to bounce between numbers so I don't want it to be turning the fan on and off rapidly if its bouncing between the temp needed to activate the fan.
You can usually set different on and off temps. Eg on at 185, off at 175. Then when it hits 175 it has to climb back up the 10 degrees to 185 before starting again.
Looking at it, you can use a resistor in parallel to reduce current. But I don't think you need to really.
Instead of a mechanical thermoswitch, you need a switched ground from your ECU. It's the same idea though. You're using a temperature triggered ground to switch the relay. The relay makes the current flow to the fan.
i have the fan control and relays tucked up in the passenger kick with the other oem bits. the resistor is mounted through the metal plate on the firewall behind the blower assembly. that way the hot bits are outside under the wiper cowl.
To save you time, lots of people have been using the same method as above but now with Nissan Quest/Mercury Villager fans and BMW thermoswitches instead of the VW/Audi one in the thread above. Your fan will be fine as long as it has enough CFMs, but the nice thing about two speed fans is that you get less draw when you don't need all the capacity during normal driving. Great if you're running stock alt.
i have the fan control and relays tucked up in the passenger kick with the other oem bits. the resistor is mounted through the metal plate on the firewall behind the blower assembly. that way the hot bits are outside under the wiper cowl.
ok so I have everything wired up but im having some trouble. im getting power from the switched side of the relay (the fan side) but the ECU issnt giving power to activate the relay. I back probed the pin out for the fan relay and when the ecu is on and the fan is switched i only get about 300mv's or so. whats the deal? Microtech on my laptop says aux #2 on which is the fan but why issnt it giving power?
If it's switching ground then you need constant +12V to the one side of the relay coil, and the switched ground to the other side.
not sure, but if that is the case, how would I wire that up? battery - fuse block - relay - ecu - ground? and how much current would it draw? 3-4 amps? Im trying to use the stock fuse block because there is an extra slot for a fuse so I dont have to add another stand alone case. the unused slot in the fuse block im using for the fan fuse.
The coil draws mA, very little current. I don't know if it even needs a fuse, someone else who has a Microtech should be able to answer. You will of course need a fuse on the fan side.
Assuming the Microtech switches ground (and not power), then you want the output from the Microtech going to one side of the coil and constant 12V going to the other side. When the Microtech switches ground it completes the circuit and activates the coil, which then activates the fan side. On the fan side it should be unchanged: +12V from battery to one side of the relay (switch side), then the other side of the relay to a fuse. Then fuse to the +12V side of the fan motor, and the negative side of the fan motor goes to ground.
The coil draws mA, very little current. I don't know if it even needs a fuse, someone else who has a Microtech should be able to answer. You will of course need a fuse on the fan side.
Assuming the Microtech switches ground (and not power), then you want the output from the Microtech going to one side of the coil and constant 12V going to the other side. When the Microtech switches ground it completes the circuit and activates the coil, which then activates the fan side. On the fan side it should be unchanged: +12V from battery to one side of the relay (switch side), then the other side of the relay to a fuse. Then fuse to the +12V side of the fan motor, and the negative side of the fan motor goes to ground.
could I splice the 12V wire I have for the fan side to work with the coil side? or would that not be wise? I'd like to use as little wire as I can just to keep it as neat as possible.
I see no reason you couldn't, they both go to the battery.
I spliced the 12v wire to connect to the coil and switch side of the relay and the fan fired right up. nowI just need to find a way to fuse and power the pusher A/C fan and make it so the engine bay doesn't look more ugly than it already is
10-21-21, 06:35 PM
