Thread: Duel fan setups how-to

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  1. #1 Duel fan setups how-to 
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    OK, so there are a few write-ups on the internet about replacing the clutch fan and "AC fan" (which is referred to below as the electrical fan) to a dual-fan set-up. These range from a full-on professional style with extra relays, to the redneck style 'run a fat wire to a switch on the dash'. We decided to go somewhere in between. Use this write up in addition to the other write-ups out there, because this write-up is not a full set of instructions!

    This electrical write-up is relevant for a 1996 240sx SE; other years may have different stock setups so double check everything before you try this on a non-1996. We used the twin-fans from an Altima; not sure what year but your twin fans may be different. (we had to dremel the edges of the twin fan, but that part of the install is not described here).

    IMportant things that you will need to know (this probably applies to other year models too, but this write-up is 1996 specific).

    Each fan on the twin fan has two pairs of 2 wires going to it (4 wires to each fan). If you connect 12v across one (any) pair of wires, the fan will operate in low speed. If you connect 12v across both pairs of wires, the fan operates at high speed. (obviously you have to test each pair to make sure you get the fan turning the right way when you connect both sets of wires!!).

    The electrical "AC" fan on the 1996 also has two sets of wires so it can operate in high speed and low speed mode.

    The electrical control for the fan on the 1996 is via two sets of 30amp relays, marked Fan LO and Fan HI. ONE relay (LO) operates for LO mode, and BOTH relays operate for HI mode.

    The electrical "AC" fan is not just for AC!!! In stock form it operates separately from the AC too:

    1. With the AC 'off', the fan will be triggered into LO mode by the ECU when the coolant temp reaches 203 degrees F and HI mode at 212 degrees. Below 203 the fan will be off.
    2. With the AC 'on' the fan will operate in LO mode below 203 and HI mode above 203.
    3. In certain situations (usually AC full on) the fan will operate in HI mode at all coolant temps.

    One last thing - each fan draws about 6 amps in LO and 8 amps in HI mode.

    We decided to use the existing wiring and relays for our twin fan setup, in order to take advantage of ECU control of the fans based on coolant temperature. This also means that the fans dont operate all the time! The wiring colors were different between the old AC fan and the new twin fan, so we made a note of the connector wire colors where the "AC fan" connects; two wires are black for -12v (ground) and the other two are for LO (one) and HI (both). We also tested for a while with some jumper wires to the battery to work out which direction the fan turned etc. We also noted all the wire colors for when we hooked it back up.

    We cut the connector off the old AC Fan, and connected it to the new twin fans (see below) so we could remove the fans from the car in future without cutting wires.

    We wired a *single* set of wires from *each* fan (i.e. two + wires and two - wires) to a single pair of wires at the connector; we then wired the remaining two sets of wires to the other pair at the connector. (note that on our connector the pairs were diagonally opposite - study yours carefully so you know where the pairs are). Remember each fan needs 12v across one set of wires for LO and *both* sets for HI.

    With this setup, both fans will operate LO at the same time, and both HI at the same time.

    On initial testing, with the car at idle the fans will come on about once a minute for about 15 seconds.. they work great!

    (pics tonight, pm me if anythig is confusing, my dad did the write up )
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  2. #2  
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    Way too much typing

    Wire both fans to a basic 4 or 5 pin relay to have them come on with the ignition

    That may seem like a waste, but with Altima fans, you lose all your shrouding that the car has stock, which pulls a vacuum around the radiator and forces air through the radiator.

    So, without the shrouding the fans need to work a lot harder to get the coolant just as cool. Having the fans come on at a low speed is pointless really.
    Last edited by Slip N Slide S14; 07-24-2008 at 03:56 PM.
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  3. #3  
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    Quote Originally Posted by Slip N Slide S14 View Post
    Way too much typing

    Wire both fans to a basic 4 or 5 pin relay to have them come on with the ignition
    were past pre school come on now :P this is for people who want to do it without them coming on full pelt all the time like they would just wiring it with the ignition.
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  4. #4  
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    oooooh

    We're past pre-school

    Im glad you know what works well then, good luck with coolant temps in humid GA temps with an A/C car.

    BTW, so you know, the temp gauge on the dash of 240's is useless, if you ever see the needle move towards the H, its already overheating, the needle only has 3 positions, its no linear in anyway.
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    Quote Originally Posted by Slip N Slide S14 View Post
    oooooh

    We're past pre-school

    Im glad you know what works well then, good luck with coolant temps in humid GA temps with an A/C car.

    BTW, so you know, the temp gauge on the dash of 240's is useless, if you ever see the needle move towards the H, its already overheating, the needle only has 3 positions, its no linear in anyway.
    lol mine is. me and my dad looked it up, trust me this way works ive tested it (And just tested it this lunchtime around 2pm) (rly rly hot >.<) and kept y car cool

    idk whats going on chad but u sure were nice when u were selling me the car...
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  6. #6  
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    Ha i am nice

    Im trying to tell you what works

    The stock 240 gauge does not tell you when the car is getting hot, it only tells you when the car is overheated and too late.

    At the least you should just have the HI speed come on both times instead of the LO speed at all.

    Im just saying, without the shrouding, the fans dont work as well, no one realizes how important the shrouds are.
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  7. #7  
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    the altima fans i used came with shrouds, i kept it nice and tight to the radiator, and compared to the clutch fan these things pull in about 3 times as much as as the stocker did (tested with my hand in front of the radiator btw..). even if the temp guage on the dash doesnt work, the fans are controlled by the ecu, and the thermostat is telling the ecu if its hot or not.
    if it gets hot on my dash im screwed with or without these fans lmao. (found that out when the water pump went pop xD!!)
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  8. #8  
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    Actually though,


    There is no fan setup that pulls more air than the stock mechanical fan and the stock shroud, that is proven.

    And when i say shroud, i am meaning all the little plastic pieces with the foam attached that go all around the radiator, the fan can be as close as you can get it, but without an actual "seal" you lose the vacuum affect.

    Look at a good pair of flex a lite fans and you will see the seal i am talking about

    Im just trying to help here
    Last edited by Slip N Slide S14; 07-24-2008 at 04:41 PM. Reason: Automerged Doublepost
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    Quote Originally Posted by Slip N Slide S14 View Post
    Actually though,


    There is no fan setup that pulls more air than the stock mechanical fan and the stock shroud, that is proven.

    And when i say shroud, i am meaning all the little plastic pieces with the foam attached that go all around the radiator, the fan can be as close as you can get it, but without an actual "seal" you lose the vacuum affect.

    Look at a good pair of flex a lite fans and you will see the seal i am talking about

    Im just trying to help here
    i understand on the help part...
    mine didnt have a seal... o.o maby thats why i feel more air??? its easy to take the fans out so maby ill try to get some foam stuff to seal it and add to said write up thanks for the idea
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  10. #10  
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    pics would help..
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