I have been looking for a point to take the electric from for a fan I am fitting to the Auto trans cooler I have, and looking at the cover for the fuse box and relays under the hood and the lid shows Rad Fan as one relay and below that it has a Sub Fan relay. I only have one fan, the rad fan so what is the other for perhaps I can use this sub fan relay? Anybody ?
There are two fans, the main fan behind the radiator and an extra fan in front of the radiator. the one in front only comes on under certain conditions. if it has been removed you need to replace it
So you have no sub-fan in front of the condensor? If you pop the bonnet and look down in front of the radiator support, you should see a small thermo fan. Your sub-fan really control's this.
Don't use the sub fan relay for power.... if you are looking for "full time" power for your auto gearbox cooler fan then DON'T use the sub fan relay, it only switches on the sub fan at high temps or very low speed. It is basically just a backup fan for you aircon condensor. If you only wish your auto cooler fan to work at high temps and/or low speed then it would be ideal. I think the relay kicks in at +220deg F or below 25mph and +190deg F on a TT.
there should be "full time power" at the Sub fan relay. The ECU switches the ground signal for the relay.
make sure however, that you get your "Power" and "control" contacts wired properly if you are going to parallel your oil cooler fan from the Sub fan relay. Pull the relay, and check your pin layout, should be marked on the side of the relay. 2 contacts will be for Power- from sub-fan fuse, through contact and to +ve terminal on sub fan (located in front of radiator, accessible under nose panel) The other 2 contacts will be for Control- as in the relay Coil. Not 100% on fuse location, but usually of a much lesser gauge/current carrying capacity wire. Will run through the coil to ECU, which switches the ground, completing the circuit for the coil and pulling in the relay contact, engaging the sub fan. You want to tap your Oil Cooler fan into the Supply side of the Relay Power contact, and you want to use the control line side (the powered side of the coil contact with relay PULLED for your control of your oil cooler fan (switch or Electric thermistat). Couple of things to consider with this approach however- i.That the COMBINED current rating of your existing sub fan and your proposed oil cooler fan DO NOT EXCEED rating of Sub Fan Fuse. Is not a simple matter of putting a larger fuse in there. Generally, you will find that the harness is sized for ratings of factory items, and rarely have the flexibility to parallel, ultimately doubling the load. Simply replacing the fuse with a larger size WILL cause an electrical fault/failure/FIRE. ii. It is VITAL that you get the correct wiring when parallelling off of an existing relay in the harness. Getting your Power and Control points arse about will result in failure. iii. Definitely incorporate an additional relay into your circuit, with adequate fuse protection. Do not undersize your wiring, and make sure that it is flexible wiring, not hard drawn. With ALL of that in mind, can strongly recommend that you run a new wire from your battery, incorporating a fuse AS CLOSE to the battery as possible. From this, you can supply BOTH your Power and Control circuits for your proposed Oil Cooler Fan. Some relays come with spade fuses incorporated into them, still ensure that you use a fuse at the battery. A short causing insulation melting and earthing to the inner guard will render a fuse further down the line useless.
Can't you just buy a temp sensor that replaces/screws into the drain plug on the transmission, you could use something like that to trip the fan on at a temperature set by you.
Could, but would suggest that consider he is installing a cooler and fan at the front of the car, that a sensor located in that vicinity would be preferrable for reducing wire lengths and routing. Unless he has a temperature gauge for the gearbox oil temperatures, would recommend using a thermo controller that has a controllable switching temperature (potentiometer). Without a oil temperature gauge, he'll be guessing as to what temp rating thermo switch will be required. Cant really see it being a problem measuring oil temps at the box or the cooler, considering that the temperature itself isnt that vital, merely that when it is "considered" to be excessive, that the fan engages. This being the case, to ascertain that the fan is in fact beneficial, suggest keeping the control as basic as possible eg- wiring to a switch inside the cabin without even mounting it in. (Can sit in Passenger side footwell). No point in going to excessive trouble only to find that the fan isnt sufficient.
Just tap into the power side of one of the fuses such as ABS or Eng Cont and use that as a trigger wire to a relay with a direct fused connection to the battery. The trigger draws SFA current and is directly linked to ignition.
yes I have 2 fans One electric in front of the radiators and one mechanical belt driven fan behind. 2 Relays one rad fan and one sub fan yet I only see one electric one ?
No, the Sub-Fan relay caters for high and low speed on the TT. To be honest, I don't know what that other relay does.
Aha !! I have found out what a sub Fan relay is there for.... Turbo models have the extra fan relay because there are two outlets from the ECCS number 6 & number 19 The fan is controlled by the ECU and corresponds to the speed, temp and Air con off or on. NA models have on and off, but the turbo models have on High, on Low and off. The sub fan relay operates the low fan speed which comes on at 90 degrees temp and the rad fan relay operates the high speed which comes on at 100 degrees both below 39 kmh. Which means I cannot use that relay, but can use the power for the control of the new relay which will be controlled by the SAW unit which I have discovered has an outlet for the fan operation. Sorted.
