Using the Idle switch to turn on cooling fans

[viprez586]

Today I had the great idea. So I began to look at the idle switch schematics. When the throttle plate is open, the idle switch should receive system voltage via the green wire coming into it. It however does not receive voltage with the throttle plate closed, which makes things tricky.

The thermosensor in the bottom of the radiator is a simple switch, there is no load(amperage), or voltage. The sensor simply heats up to close it's internal contacts and completes the circuit for the cooling system relay(s) to feed power to the fans.

Since the thermosensor is a simple switch I'm hesitant to just splice into the IPS wire. I would like to somehow incorporate a relay into both systems so that when the throttle plate closes the fans kick on yet also have a manual switch to kick on the fans while in slow traffic (stop and go).

I currently just ran two wires from the thermosensor connector and tossed my thermosensor(it was junk anyway). I then fed the two wires to a simple rocker switch in-cabin to manually turn on the fans when I want and if I remember to.

Open to ideas here but please don't reply if you don't have a basic understanding of whats going on here. Thanks guys!

Edit* found a good thread that might have some helpful info/hints. http://www.dsmtuners.com/forums/articles-electrical-wiring/269939-how-turn-cooling-fans-motor-running-key-removed.html

 

[yokotabrat]

It's not so much that the idle switch is providing a voltage when it's off, it's more the grounding that will work for what you want to do. The easiest way is to use a simple relay. Connect one end of the energizing coil to the idle switch wire. The other end you want to connect to a voltage source, but you'll have to be careful here. Internally on the ecu, there should be a pullup resistor on that line. Whether it pulls up to 12 or to 5V, I'm not sure. You'll need to match whatever voltage you measure when the throttle is open with the relay coil, otherwise you'll potentially damage the ecu.

Once you have that figured out, just connect the normally open side of the relay and the common side of the relay to the 2 terminals where the thermo switch used to be.

That should be it.

 

[steve]

Today I had the great idea. So I began to look at the idle switch schematics. When the throttle plate is open, the idle switch should receive system voltage via the green wire coming into it. It however does not receive voltage with the throttle plate closed, which makes things tricky.

The ECU pulls the IPS signal up and senses the voltage so that it knows when the IPS grounds the input and pulls the voltage down. The current is limited by the pull up resistor in the ECU.

The thermosensor in the bottom of the radiator is a simple switch, there is no load(amperage), or voltage. The sensor simply heats up to close it's internal contacts and completes the circuit for the cooling system relay(s) to feed power to the fans.

Wrong, the thermoswitch passes the current needed to activate the relay when it closes and has 12v across it when it's open. So there is both voltage and current.

Since the thermosensor is a simple switch I'm hesitant to just splice into the IPS wire. I would like to somehow incorporate a relay into both systems so that when the throttle plate closes the fans kick on yet also have a manual switch to kick on the fans while in slow traffic (stop and go).

You shouldn't just splice into it. You could damage the ECU. You can sense the the voltage yourself and drive a relay or possibly put a diode in the ECU wiring and another in a relay circuit and use the IPS to ground both the ECU and the coil of a relay to run the fan.

I currently just ran two wires from the thermosensor connector and tossed my thermosensor(it was junk anyway). I then fed the two wires to a simple rocker switch in-cabin to manually turn on the fans when I want and if I remember to.

Open to ideas here but please don't reply if you don't have a basic understanding of whats going on here. Thanks guys!

Another option is to put a real temp sensor in the bottom of the radiator and use it to control when the fans turn off and on rather than the fixed temp the thermoswitch used.

 

[viprez586]

Wrong, the thermoswitch passes the current needed to activate the relay when it closes and has 12v across it when it's open. So there is both voltage and current.

Yes for lack of better wording on my part - I stand corrected.

You shouldn't just splice into it. You could damage the ECU. You can sense the the voltage yourself and drive a relay or possibly put a diode in the ECU wiring and another in a relay circuit and use the IPS to ground both the ECU and the coil of a relay to run the fan.

That's something that i had in mind. Perhaps a wiring schematic to clarify?

Another option is to put a real temp sensor in the bottom of the radiator and use it to control when the fans turn off and on rather than the fixed temp the thermoswitch used.

Please elaborate. Know of a thermoswitch in mind?

 

[knochgoon24]

Go to your local auto parts store and look near where they have all the transmission fluid coolers. There will be thermoswitches there. Some are fixed temperature (usually 185* or so) or adjustable.

 

[steve]

Know of a thermoswitch in mind?

Something like this Fan controller Derale Deluxe Adjustable Controllers with Pipe Threaded Probes Fan Control - Thermostatic - Adjustable - 150 Degrees On - 240 Degrees Off - Kit | StreetPerformance.com

 

[1fast97gsx]

Why not just let your computer do it for you ... what is the purpose of this???

 

[steve]

Why not just let your computer do it for you ... what is the purpose of this???

The ECU doesn't control the fans on a 1G. So it's hard to just let the computer do it.