Guide - How to wire up thermofans

[The Witzl]

This if for all the people who keep asking...

The Witzl's Guide to Wiring up thermofans

well here you are....

Note regarding thermoswitches: Most toyota thermoswitches i have tested are norally closed type.... meaning that they are connected to earth until they reach a set temperature and then open that connection..... thus if you unplug the wire to the thermoswitch the fan will begin to operate. This is a failsafe for if your switch dies on the inside it will just run the fans permanently....

You can use an aftermarket thermoswitch, just make sure its a normally closed type for wiring it up in this method i am outlining.


Version modified by Mos (acknowledged by Witzl).


And here is the less technical diagram, courtesy of Witzl Inc Graphic Design Studios (aka "TA-022" - Nathan)



This is an example of a Toyota Thermoswitch with the blue wire coming out. Found VERY commonly in wreckers in SV21, SV11, AE82, AE92, ST162 etc etc





Additional information by Mos:
Below are the standard relays commonly available - all have pins 85 and 86 as the solenoid, and applying power across those pins activates the relay.
The first is a 4 pin, normally open type, with an input on pin 30 and a single ouput on pin 87.
The second is a 5 pin, normally open type, with an input on pin 30 and two outputs on two pins marked 87.
The third is a switching or "change over" 5 pin, with an input on pin 30, a normally closed output on pin 87a and a normally open output on pin 87. Sometimes the "a" is printed away from the 87 and is not immediately obvious.



A setup using a Normally Closed thermostat should be something like this:


A setup using a Normally Open thermostat is a lot simpler than a NC setup:



*** Mos additions verified by Witzl. Thanks Mos

[bbaacchhyy]

Witz,

I have managed to complete my thermo fan wiring, and ended up using a switch that is normally open, and whilst there are several options out there, they are either expensive or on rare vehicles. The one that was best suited was from an Avalon, but sadly, they are over $100 a pop and there aren't many at the wreckers.

My wiring was similar to the above but reflects the different thermos witch used, but your guide was agreat help !!!

Cheers

Michael B

[ed]

ive got a few variations on witzl's one...

first up, i run my switch on the rad bottom tank/outlet: i think its wiser to have the fans switched on and off based on how the radiator is performing - not on what the output temp of the engine is. after all, isnt the fan supposed to assist the radiator function? and what better way to measure it? if the output temp of the engine is too high, and you know the raditator is working properly (+- fan assist), then theres something wrong with the cooling system, not the way you switch your fans on and off...

anyway, to do this is use a normally open 2 wire thermo switch, as is easily sourced from the bottom rad tank of practically any 90's mitsu magna. on at 85 and off at 75 if i remember correctly

secondly, if i run two fans, i run them on two independant circuits, with their own relays etc, just incase sommething fucks itself

and finally, i run a thermoswitch override switch inside the cabin, so if everything goes to hell for some reason, i can still manually switch the fans on and bypass all wiring.

cheers
ed

[bbaacchhyy]

I sorta agree with you there Ed, but isn't it interesting that most of the manufacturers don't do it this way ? I'll ask the HVAC guys next time I get a chance.

I have the fans wired to separate relays, and will add the cabin switch as you mention. Might even use the A/C switch for this very purpose !!!

Cheers

Michael B

PS The GTO fans are wired such that they can either have one or both switched on - controlled by the ECU.

[Mos]

The above setups don't take into account running A/C for those of us who choose to retain some comfort It would take a great deal of time for the water temp switch to "see" the rise in refrigerant pressure due to insufficient air flow. The A/C high pressure switch could be run in series with the water temp switch to allow some fan functionality for the A/C.
The "traditional" toyota setup involving two fans runs the fans in series at low speed when the A/C is activated and the radiator is under temperature. If either the A/C high pressure switch activates, or the radiator temp switch activates, the fans run at full speed in parallel.
The setup usually has a single common supply relay (usually the engine main relay) with two individual relays controlling the switch on for both fans. The fourth relay activates the parallel function.
It would be interesting to find out the relationships between the temperatures at the four possible cooling system locations where one might insert a temperature sensor. Are there any toyotas with this sensor in the top side?
Mos.

[Steve-AE86]

is it just me, or does the 'thermostat' in the top pic look like a bong? :s

[oldcorollas]

is it just me, or does the 'thermostat' in the top pic look like a bong? :s

might just be you.....

anyway,
http://members.optushome.com.au/mkha...elay_diags.pdf

not as elegant as witzl design, but simpler.

[wagonist]

Mos, have you got a wiring diagram for the circuit as you've described?

Can it be used like this for aftermarket fans, or is it Toyota only?

[BradW]

might just be you.....

anyway,
http://members.optushome.com.au/mkha...elay_diags.pdf

not as elegant as witzl design, but simpler.

Those diagrams appear to be for thermoswitches that close circuit when the "high" temperature is reached (ie normally open) whereas the toyota thermoswitches are, as The Witzl stated, normally closed and go open circuit when temp is "high".
Also it shows the 87a terminal as n/o when 87a is a n/c contact.
Sorry to be picky . They are simpler though .

[Mos]

Mos, have you got a wiring diagram for the circuit as you've described?

Yes, I do, but not online unfortunately. I'll try to get something scanned but it won't be a priority I'm sorry.

Can it be used like this for aftermarket fans, or is it Toyota only?

You can use it on aftermarket fans also, although if they're heavily mismatched you can get unpredictable effects. The two aftermarket fans on the sprinter were wired in such a fashion.

Mos.

[Mos]

Those diagrams appear to be for thermoswitches that close circuit when the "high" temperature is reached (ie normally open) whereas the toyota thermoswitches are, as The Witzl stated, normally closed and go open circuit when temp is "high".

Interestingly enough, in contrast to the majority of earlier toyota thermo switches, the IS200 uses normally open switches, ie they connect to activate the fans. I wonder if that's representative of the newer models.

Also it shows the 87a terminal as n/o when 87a is a n/c contact.
Sorry to be picky . They are simpler though .

Given that the terminal labelled 87a goes to an indicator light I'd say it should actually be labelled as 87 rather than being a n/c contact. The "standard" 5 pin relays are available with two 87 pins for appropriate applications rather and an 87 and an 87a - the relay pinout appears to be confirm this.

And yeah, much simpler

Mos.

[bbaacchhyy]

Well, I have finally gotten on to the HVAC dude, and had an interesting conversation regarding the good bits about the cooling systems and thermofan theory and some of the current trends.

First off, as discussion on the placement of the thermofan switch. Typically, it is now done from the Eng coolant temp sensor and a signal is sent from the ECU rather than a separate switch. Whilst the theory of what Ed mwentioned is OK, the time lag experienced would be minimal. As an example, a V6 Crumpledore, the coolant flow rate through the CRFM is between 20 l/min (idle) to 180 l/min (flat knackers) with a typical flow of 80 l/min. So you can see that even if the thermo switch is on the clod side, the time lag is not that great. Whether it works better or not is another thing. That is the design that most companies use.

New developments though is the shift for the thermostat to be on the cold side of the engine. The reasoning is apparently better engine temp control, but introduces a number of headaches into the system. The coolant temp sensor is still on the hot side. This is the path being chosen by GM and Ford and others, and one of the side aspects is that there is a need for a pressurised surge tank to aid in the filling and degassing of the systems based on the thermostat location. The system fill in plant is done by sucking air out of the systems, and then forcing in coolant (set volume) under pressure to ensure that all (or most) of the air is taken out of the system.

The next thing is about how a set of twin thermo fans should be setup, and what the idea/temps behind the temp switches that control them, but that will be another post when I have a few more moments.

Cheers
For now

Michael B

[The Witzl]

I am considering the use of a PWM speed controlled thermofan on the RA28's 18RG, using a temp sensor with a suitable temp range/output to somehow act as an input to the fan speed controller.

Of course this is silly and completely not worth the effort... but then again i am a silly kind of guy!

[bbaacchhyy]

More as promised.......

OK, now for part two.

I am waiting on some info from the HVAC dude, but I got some interesting stats regarding the temps at what you switch on the fans at. Largely they back up previous numbers quoted in other discussions, but basically the values are such.

For fans running single speed (twins or singles) : Aim for a “temp on” temperature about 10 degrees above thermostat open, and a ”temp off” temperature of 5 degrees above the thermostat temp. This way, you allow for hysteresis of the various temp controlled items, and you also don’t end up with the fans and the thermostat fighting each other at a switch over temp.

For fans running twin speed (twins thermo’s ala AU Ford etc) : The basic set-up is to have the fans run in two modes – Low power and High power. This can be done in a few ways, but the Ford and Holden version is similar (I’m waiting to get the cct details so that I can share this info). The low power setting involves running the two fans together in series which means that both fans only see 6V and therefore only give about 35% of their cooling capacity. With the fans run in parallel, both see 12V, and give 100% cooling capacity.

The switch set-up is that you either run two switches or use a switch that has both internal contacts in it (apparently the JD Vectra has this set-up as do others). For a thermostat of 90 degrees, the low power switch would have the same temps as listed above (fans on at 10 deg above thermostat, and off at 5 deg above thermostat), and for the high power setting, you would have an on temp of 110 degrees and off at 105 degrees, and this allows for a 5 degree hysteresis once again.

The High/Low power set-up is best for DD cars, whilst if the car is an occasional fanger, it is not so important. Part of the main basis for the high/low fan speeds is that when the temps rise and the fans switch on, the engine doesn’t see a huge slug of cold(er) water and then shut the thermostat and you end up with a bit of temperature hunting, but instead you get a gradual cooling that keeps the temperature much more stable.

As soon as I get the info, I’ll try and post it up.

All makes sense to me

Cheers
For now, again

Michael B

[CrUZida]

A lot of the above has seemed to gone over the top (as most tend to do on Toymods).

In my setup, I have a Tridon temp switch (95on, 90off), that switches a Nissan relay (two independant in/outs with a single switch), and the AU thermo's.

Since I have auto, and am running an auto cooler (not the radiator one), I found it was getting very warm at idle after I went from viscous fan to the thermo's.
So I installed an old MA61 aircon fan infront of the auto cooler, which is TPS switched.
When the TPS is in IDL, the fan is on, when the TPS is anywhere else, the fan is off.

This ensures that the tranny cooler is getting moving air at all times while the car is stationary.
Also, thus far, this small amount of air has been enough to keep the motor below 95deg where the thermo's kick in, as they haven't turned on at all in the last few months.

Will be interesting to see how it goes in summer, but I am now confident that I can sit at traffic lights in gear on a 40+degC day and not have any cooling issues.

Aircon is not plumbed yet (its coming) so I don't know how that will go, but I suspect the auto cooler fan I've installed will help there.