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Thermofan wiring-THermistor help

Discussion in 'Electronics' started by dan1_721, Apr 14, 2008.

  1. dan1_721

    dan1_721 Guest

    Ok, since I cant seem to get my fans to turn off, even though iv changed a few sensors and relays, Id like to rewire it using a seperate relay, the factory switch in the thermostat housing, and still have the AC trip the fan, or however it is meant to work. Possible?
     
  2. cannon

    cannon Guest

    not possible the facory thermostat housing is not electronicall sensed is spring operated not electronically get an electronic thermostat hook it up to a relay
     
  3. dan1_721

    dan1_721 Guest

    Cannon, there is a sensor mounted above the thermostat in the housing, it is a thermistor, and sends the signal to the ECU about whether to turn the fans on I believe. It is electronic, and the themostat itself has nothing to do with it.
     
  4. cannon

    cannon Guest

    well what id do is try and make it bypass the ecu because its not really necesarry for it to be going through it and have the thermistor wired straight to the relay for the fans and test the themistor with a multimeter see if it works properly. see if that works. if i were you, scrap the stock cooling circuit system, wire them directly to the battery. as it is from the factory when you turn the ignition copletely off the fans will not work. i like to have them running after my car is switched off to cool it down a bit more a afdter you switch your car off. thats how i did it on my old corollas thermo fans. i bought a temperature switch kit from jaycar it cost me $30 and i had the thermistor mounted directly on the radiator core close to the bottom hose. i had two relays one to switch the thermos on and off, and another to switch an indicator light that i put on my dash to tell me whether they are on or off..hope this gives u a bit of an idea
     
  5. dan1_721

    dan1_721 Guest

    http://i269.photobucket.com/albums/jj52 ... ayidea.jpg

    I have made this crude diagram :D to show my idea

    I think I would simply use a thermistor with the right characteristics as shown to switch the fans on. I would just have it glued to the inside of the rad hose i guess...

    Just need help knowing what thermistor to use...

    then it would be auto controlled due to temp, the factory control would be left alone, and i could switch them on manually. Dont really want them running at all after the car is off, the power they use is huge....
     
  6. cannon

    cannon Guest

    the diagram looks like it will work fine. yeah i was going to put mine inside the rad hose, but i didnt want to lose the strangth in the hose.. get the one from jaycar, its only $30, its awesome comes with a adjustable temp sensor, relay, relay plug & mount, fuse block and enough wire to do the job and you can adjust the temperature at which it cuts the fans off and on at! i think its called a thermo switch kit or something like that
     
  7. dan1_721

    dan1_721 Guest

    Dont you have to solder it and put it together and stuff though?

    Id rather just have the thermistor do it automatically, out of sight, out of mind, standard looking. Doesnt appeal having an aftermarket fan controller, whether inside the car or engine bay or whatever.
     
  8. cannon

    cannon Guest

    its in the engine bay. what i meant was once you set the temperature at which the thermistor switches at, you leave it alone. just depends on what temperature you want your car running at.
     
  9. dan1_721

    dan1_721 Guest

    Help...

    Just need someone to help me with the thermistor part, as in whats an appropriate temp for the fans to switch at, and im sure theres a way to calculate roughly what thermistor value would be needed? I have no clue haha.

    This is how I want to do it anyway....The switch will be mounted discretely inside the car.

    Also forgot, I will need to add a trigger from the ac, to turn both the fans on also. Im going to control them together, but obviously they need to come on with the AC. Where can i tap a trigger from for this?
     
  10. cannon

    cannon Guest

    on the ecu, there is a positive trigger for the AC it in on the 3rd plug (closest to the gearstick) 8 pins from the edge on the bottom row so X is where it is located just add it to the relay trigger pin

    FIRST PLUG|SECOND PLUG|000000000000
    FIRST PLUG|SECOND PLUG|0000X0000000

    use a normally closed relay for the thermistor and the fans should switch on (no thermistor continuity) when the coolant temp is above 93*C and turn off when below 83*C (must be thermistor continuity)there must be a 10 degree gap to prevent it from erratically switching on and off

    those temperatur figure was out of the 3sge manual
     
  11. cannon

    cannon Guest

    also the coolant temp sensor is at
    FIRST PLUG|00000000X|000000000000
    FIRST PLUG|000000000|000000000000
     
  12. dan1_721

    dan1_721 Guest

    Dont get how that will work....
     
  13. cannon

    cannon Guest

    well the NC relay is connected so it has power as long as the ignition is on, BUT since the thermistor is connected inline with the relay, it will be switched off when there is continuity through the thermistor.

    the thermistor lets voltage pass through it when at low temperatures, switching the normally closed relay off, in turn switching the fans off.

    when the temperature rises above 93*C, the thermistor will cut power to the relay coil, sending the relay back to its normally closed position, switching the fans back on.

    by the way, you wont be able to hook the AC trigger from the ECU to the NC relay, otherwise it will switch the fans off when the air con is on, so you must run it to a 2nd relay that is N/O but in a separate circuit that is not in series with the other

    sorry for the vague explanation, do you understand how it will work now?
     
  14. dan1_721

    dan1_721 Guest

    So each relay would be connected to the fans on its own. The NC would be connected how? As normal but with the trigger line to the ECU pin?

    And the NO would of course have a trigger line running off a switched acc line, and with the AC trigger added in.

    If I got the wiring idea for the NC relay wrong, make a crude diagram haha. Cheers!
     
  15. dan1_721

    dan1_721 Guest

    Im guessing, that on this page, the normally closed realy is the "change over" relay, as looking from the diagram, its closed....correct?

    This could be easy.....ONly part is figuring out what contacts on the relays connect to what...
     
  16. cannon

    cannon Guest

    yep correct heres a crude diagram just in case
     
  17. dan1_721

    dan1_721 Guest

    http://www.narva.com.au/Switches_18.html This is the "changeover relay i was referreing to.,

    Cannon, any chance you could make a clearer diagram? Including the numbered pins of the relays and their connections? Because then I would know exactly what to do...
     
  18. dan1_721

    dan1_721 Guest

    SO on the NC relay, it is connected to the thermistor wire out of the ecu loom, rather than grounded?
     
  19. cannon

    cannon Guest

    yep thats if you use the stock thermistor
     

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