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Question about wiring a fan relay

Discussion in 'The Hokey Ass Message Board' started by atomickustom, Aug 16, 2006.

  1. atomickustom
    Joined: Aug 30, 2005
    Posts: 3,402

    atomickustom
    Member

    I have a dumb wiring question:

    Forgive me if this is already on the HAMB (and please post me the link if it is), but I'm going to be wiring an electric fan with a relay, and I have one important question: does it matter if the power source is a full-time power source? The diagram that came with the relay calls for an ignition-on power wire, but I have a full-time power wire that's heavy gauge, more than enough amperage, and conveniently not being used for anything else.
    I'm not real clear on how the relays work, but I get the impression it functions kind of like a switch, and therefore it won't hurt anything to have power going to that sucker all the time, right? As long as my manual dash switch is off, the fan's off and all is well, right? (And by the way, the diagram indicates that the switch should go to a ground.)
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 48,676

    squirrel
    Member

    You can use a full time power source, just beware that the fan could get left on and drain the battery.
     
  3. Nick79
    Joined: Apr 19, 2006
    Posts: 276

    Nick79
    Member
    from Austin, TX

    Here's how I wired my fan switch.

    I used a battery feed (with short stop) to power the relay. One of the relay switch wires goes to my thermal switch (screwed into the water pump) and the other switch wire I wired to an always hot line from my fuse panel. You can use an ignition hot line or an always hot line to switch the relay, but if you use an ignition hot line, when you turn the ignition to the off position, the fan can't run. You may still boil over as the car can get hotter after shutdown. If you wire it to an always hot line, the fan can still function when the ignition is off.

    The drawback of an always hot line could be that the thermal switch fails and the fan goes on when you're not around....draining your battery. You could use an always hot line and include a switch in the dash, but you can't forget to turn the switch back on when you run the car!!

    My $0.00000000000000000000000000000000000000001
     
  4. yea the squirrel is right.
    if its a stat controlled fan it won't shut off until it satifies and if its toggle controlled it may be left on when you get where you're going eithway can leave you high n dry.
     

  5. squirrel
    Joined: Sep 23, 2004
    Posts: 48,676

    squirrel
    Member

    I've never had any problem with my electric fans since I replaced them with a belt driven fan 10 years ago....
     
  6. Retrorod
    Joined: Jan 25, 2006
    Posts: 2,030

    Retrorod
    Member

    I've had two of those expensive thermostatic switches take a crap on me....one of them right in the middle of the cruise at 'Paso. We switched over to a simple toggle and have it wired to an ignition switched lead. I was thinking of installing a small red or green mini bulb wired to the fan power circuit just to be able to check on the fan.
     
  7. Bluto
    Joined: Feb 15, 2005
    Posts: 5,113

    Bluto
    Member Emeritus

    All fans are NOT created equal. Some draw far less amps than others.

    And the price doesn't always matter.
     
  8. Steve M
    Joined: Jun 25, 2005
    Posts: 199

    Steve M
    Member

    Bluto is correct. Check out the yards for a Mark VIII electric fan.
     
  9. 12 ga wire from the battery to the "C" or common terminal (use a crcuit breaker in this circuit)

    12 ga wire from the "NO" or Normally Open terminal to the fan.

    Nothing gets connected to the "NC" or Normally Closed terminal.

    The other two terminals are used for picking (energizing) the relay.

    Connect one to the ignition switch and connect the other to ground. The size of these two wires need not be large as they are not required to carry heavy current.

    If you have a thermostat. splice it into either the ignition power wire or the ground. The fan won't come on until the thermostat clicks on AND the ignition is ON.

    Your fan will only come on if the ignition is turned on.
     
  10. The advantages to having the fan powered all the time is that it will cool the car after a run, even if you park up directly after running on the highway.
    Any disadvantage would have to do with the possibility of the fan coming on at any time.
    I, personally, wire electric fans to be powered all the time.
    Any concern that the fan would run down the battery is silly, as the fan would cool the car and be shut down loooooong before the battery would be run down.
    Cosmo
     
  11. axeman39
    Joined: Jan 15, 2006
    Posts: 423

    axeman39
    Member
    from Saco Maine

    Ok Dave, Im gonna make it real simple. go to your local radio shack or auto parts store and buy a 5 terminal common relay. The one you already have may be correct. Look at the bottom of the relay you will notice that each blade has a number next to it, they should be 30,85,86,87 and 87a in the center. Now run constant power [fused is ok] to terminals 86 and 87. Run a wire from terminal 30 to the positive wire of your fan, ground the other fan wire good. Now run a wire from terminal 85 to your switch and ground the other terminal of your switch. Terminal 87a of the relay is not used in this application. by doing it this way you do not have a hot wire running through your firewall. [wires seem to like chaffing in firewalls and grounding out causing fires] dont ask me how I know this. Flip the switch the fan runs flip it again now its off. If the fan runs backwards switch the fan wires around. Good luck.;)
     
  12. T2B
    Joined: Jul 21, 2006
    Posts: 17

    T2B
    Member
    from san diego

    axeman39 has it right. However, if you choose to use a thermal switch you can connect the thermal switch wire to the same terminal as the toggle switch (#85) Doing this gives you the advantage of turning the fan on at will or letting the thermal switch control it for you. I have been know to forget to turn the fan on. Mine runs when the key is on and stops when the key is off, no switches.
     
  13. atomickustom
    Joined: Aug 30, 2005
    Posts: 3,402

    atomickustom
    Member

    Okay, that is exactly the information I need.
    Still a couple questions:
    1. It's okay to use the same power source for both terminals on the relay?
    2. My diagram calls for the power to go to terminals 86 and 30, and #87 goes to the fan. Does it matter if I do it this way or your way?

    By the way, thanks to all of you for all of the replies and information.

     
  14. tommy
    Joined: Mar 3, 2001
    Posts: 14,757

    tommy
    Member Emeritus

    I've walked by lots of parked cars with the electric fan still running. I always wondered where their thermostatic switch was located. If it's in the radiator, I could understand but all you are cooling is the water in the radiator. If it's in the block or intake with no coolant flow, it won't cool the engine down any quicker anyway. The radiator may be cool but the engine will still have to cool down naturally no matter what kind fan you have on there. Sometimes I think it's like the automatic headlights...people just like the idea of it shutting itself off automatically.
     
  15. Sorta, but not really. The radiator DOES cool off faster this way, then a thermosyphon action cools the engine. Thermosyphon is a term describing a cooling system without a waterpump that relies on the fact that hot water rises and cool water falls. The cool water from the rad will enter the engine through the lower hose, and the hot will re-enter the rad through the upper hose. Thus your system 'flow'.
    This is how Model Ts are cooled, along with many other early engines.
    Cosmo
     
  16. squirrel
    Joined: Sep 23, 2004
    Posts: 48,676

    squirrel
    Member

    I think thermosiphon works a lot better if the engine is making heat....might not do much after you shut it down.
     
  17. axeman39
    Joined: Jan 15, 2006
    Posts: 423

    axeman39
    Member
    from Saco Maine

    Yes its ok to use the same power source for both, And as far as I was always told use terminal 30 for output. but there are several ways to wire a relay for many different applications I just know this way works perfect and Ive used it at least 100 times with no problems.
     
  18. atomickustom
    Joined: Aug 30, 2005
    Posts: 3,402

    atomickustom
    Member

    Thanks!

     

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