Guide - How to wire up thermofans

**egamirrorim** · 26-01-2012, 10:04 AM

Can anyone help?
Anyone at all...

**ballpencil** · 26-01-2012, 10:18 AM

even if the fan turns when you start, if wired correctly there won't be 11amps going through the startup circuit just like you said.

make sure to hook only the 85 of the normally open relay to the ignition. nothing else should attach to the ignition, the rest should either go to the battery, thermoswitch, ground or fan.. check the diagram again. i have used the same circuit with no problem.

**The Witzl** · 27-01-2012, 01:47 PM

Originally Posted by ballpencil

read the whole thread from the beginning and failed to find anyone mentioning the possibility of running NC thermoswitch with just 1 (one) relay..

this can be done depending on one problem which will be explained/asked later.

basically it's the same as Witzl's two-relay diagram, only you omit the first ignition switch relay like this:

this way the fan will still turn on when the you unplug the thermoswitch. however, as stated earlier, there is a problem. the relay will still be activated (pulling current) even with the engine cold and off (alternator not charging). i have to emphasize that it's only the relay activated. the fan will still turn off. as such, this diagram will work only if the current drawn by the 85-86 electromagnet coil is small enough to not be parasitic load on the battery.

mind that you're already drawing current from audio tape and ECU.

then the question would be, how much is the current drawn from 85-86 relay coil? i.e how long can you keep the engine turned off before you finally lose cranking voltage from the battery? there's even the possibility of running a serial resistor with the fuse as to reduce the current drawn by 85-86 coil.

The problem with this wiring above is that the thermofan will continue to run after you turn your car off.

That is why i have an extra relay, supplying power to the 2nd relay only when ignition is on. This way, the fan can only run when ignition is turned on.
Im not a complete idiot

**The Witzl** · 27-01-2012, 01:55 PM

Originally Posted by egamirrorim

I've just finished installing an alloy radiator with a themofan setup on my RA28, all the wiring is done for the thermofan except for one: I have a wire that needs to go to 'ignition', all of the wiring diagrams I've looked at DO NOT specify where exactly in the ignition circuit I should be connecting this to. I was going to just attach this wire to the positve on either my igntion coil or ballast resistor but my engine builder said these are both wrong. Do I have to attach this wire into the 'run' circuit on the back of the ignition key barrel?! I have an oil pressure gauge wire that needs to go to this as well, so I'm really not sure how I'm going to attach all this to such a small contact!

Please help - this is the last thing holding up my 10 month rebuild!

You need to add a relay to provide high current IGNITION power to the fan relay.

**egamirrorim** · 27-01-2012, 07:17 PM

Originally Posted by The Witzl

You need to add a relay to provide high current IGNITION power to the fan relay.

Hmmm... I dont think another relay is required: The thermo fan is a Calibre kit I bought with everything needed for installation, the wiring diagram that comes with it just has one wire going to "ignition", it doesnt mention anything about adding another relay. I'm using a normally open thermo fan switch if that changes anything...?

**ballpencil** · 27-01-2012, 09:29 PM

Originally Posted by egamirrorim

Hmmm... I dont think another relay is required: The thermo fan is a Calibre kit I bought with everything needed for installation, the wiring diagram that comes with it just has one wire going to "ignition", it doesnt mention anything about adding another relay. I'm using a normally open thermo fan switch if that changes anything...?

That changes everything. Normally open thermowitch need only one relay. That Calibre Kit already has a relay?

j

**ballpencil** · 27-01-2012, 09:37 PM

Originally Posted by The Witzl

The problem with this wiring above is that the thermofan will continue to run after you turn your car off.

That is why i have an extra relay, supplying power to the 2nd relay only when ignition is on. This way, the fan can only run when ignition is turned on.
Im not a complete idiot

Yes, my post was incomplete. I said that only the relay will be powered but that's only after the fan has finished cooling the engine, regardless ignition key position. Once engine has cooled of(f, fan will stop as well. Quite sure the battery will hold just fine with just 30-60 seconds of powering a fan without any alternator supply. The problem is if relays draw enough current to discharge the battery overnight.

**egamirrorim** · 27-01-2012, 10:06 PM

The calibre kit had a relay and had all the wires for the relay crimped and ready to go, it even had a nifty little clip with all the wires pre-attached ready to plug into the relay, it could all only go in one way too so there's no mistakes there.
I dont understand how this single relay setup is going to allow the fan to run after the ignition switch is turned off: There will only be power in the ignition circuit when the car is starting/running?!

**ballpencil** · 28-01-2012, 02:06 AM

Originally Posted by egamirrorim

The calibre kit had a relay and had all the wires for the relay crimped and ready to go, it even had a nifty little clip with all the wires pre-attached ready to plug into the relay, it could all only go in one way too so there's no mistakes there.
I dont understand how this single relay setup is going to allow the fan to run after the ignition switch is turned off: There will only be power in the ignition circuit when the car is starting/running?!

perhaps you got mixed up mate? a single relay with normally open thermoswitch just like in the Calibre kit will hook to the ignition. this setup will not run the fan after ign switch is off. a single relay with normally closed thermoswitch is not the recommended setup as this will still turn the fan even when key is off. the fan will only turn off when the engine has cooled down. this setup hooks directly to the battery and will at minimum constantly load the battery with relay electromagnet current.

**egamirrorim** · 28-01-2012, 08:00 AM

Ahh ok. Thanks!
Puts me back to square one though: just to get the car running I will attach the other side of the thermo fan switch to the coil or ballast resistor, but what is the 'right' way to wire that up? Should it really go the the back of the key ignition switch?

**The Witzl** · 31-01-2012, 10:22 AM

Originally Posted by ballpencil

Yes, my post was incomplete. I said that only the relay will be powered but that's only after the fan has finished cooling the engine, regardless ignition key position. Once engine has cooled of(f, fan will stop as well. Quite sure the battery will hold just fine with just 30-60 seconds of powering a fan without any alternator supply. The problem is if relays draw enough current to discharge the battery overnight.

Honestly - I would NOT do what you are suggesting. It is a dumb idea.
1/ The relay will draw around 0.3A continuously. Hence your battery will be flat in around 5-7 days, depending on the quality of your battery.
2/ There is no failsafe that "kills" the circuit once the car has been turned off. What if the thermoswitch fails (which DOES happen!!!), then you have your fan running 24/7.... and will have a dead battery in around 2-3 hours.
3/ The fan will be drawing around 10-15A. This equates to a dead battery within 2-3 hours.

Toyota deemed it unnecessary to "after-run" thermofans on most of their engines.... so why do you want to do it? What is going to make the engine get hotter after you switch it off??? All the sources of heat have been removed - so the engine will be naturally cooling.

If you REALLY must have the wank of an after-run thermofan.... employ a timer circuit to the thermofan, that allows no more than 2-5 minutes of operation after you turn off the engine but cutting power to the thermofan relay. This will provide the "kill" to this circuit that will protect your battery.

Originally Posted by egamirrorim

Ahh ok. Thanks!
Puts me back to square one though: just to get the car running I will attach the other side of the thermo fan switch to the coil or ballast resistor, but what is the 'right' way to wire that up? Should it really go the the back of the key ignition switch?

Now i understand... In your calibre thermofan kit you have a normally open thermoswitch, so yes, only one relay is required.
The ignition wire in your system will only be provided minimal current to close the relay contact.
I assume that the kit also has a thicker wire with a fuse, connected to the POS battery terminal - this is where the current will be drawn from.

Hence, it is fine to source ignition from the ignition coil POS terminal, cos this is an easy spot to hook up to.