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Location:
Terrigal
Registered:
May 2002
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4AGE thermo fan switch wiring
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Sat, 13 November 2004 04:09
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Hello, I need some help wiring up a factory toyota thermo fan temp switch.
The thermo fan switch is earthed until it reaches the set temperature.
The relay for the fan is the design that is held open by the earthed thermo fan switch then when the switch gets
to a certain temp it isn't earthed anymore and the relay then is closed and supplys power to the fan.
Problem is I got no idea how to wire this up..
I first thought -
thermo temp switch to the relay coil and then ign + on the other side of the coil. Then batt + and +ve wire to thermo
fan on the switching side. So the temp switch and ign + would keep the relay open so the fan wouldn't be running
and then when is closes it the fan will run.
That would work except when ignition is off, the fan is always running.
I thought another idea the same as the above but apart from ign + to the relay coil, run batt +. This works fine,
except that will leave a drain on the battery as the relay will constantly be held open even with the car off.
So yeah I just cant see how this works. Maybe 2 relays are needed somehow??
In the past i've always just used the thermo temp switches that connect to ground when they reach a set temp and that
is easy to wire up to a relay. But I really want to get the factory toyota one working.
Any ideas???
Thanks!
Joel
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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: 4AGE thermo fan switch wiring
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Sat, 13 November 2004 05:03
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what you need is a relay with NORMALLY CLOSED contacts.
A jaycar SY4070 will do the trick.
How this works is that when there is no 12V across the coil terminals, then the common terminal is connected to the centre terminal (aka - NORMALLY CLOSED/NC).
When 12V is applied is applied across the terminals, then the relay activated and the COMMON terminal connects to the NORMALLY OPEN/NO terminal.
Hence......
# Wire the temp switch to one side of coil
# Wire power feed to the common terminal - but use a second relay triggered from IGN to supply power.
# Wire other side of relay coil to IGN
W wire fan power wire to NC terminal on relay.
Easy peasy.
Toyota gets away with using customy relays that have dual contacts with the above system - as they are all in the one fuse box you see? If you are referring to the AE86 - you might even have the spot in there for this already....
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Location:
Terrigal
Registered:
May 2002
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Re: 4AGE thermo fan switch wiring
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Sat, 13 November 2004 05:45
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Thanks for reply Witzl, yeah i've got the original Toyota relay that when no power applied to the coil the switching side of the relay is connected.
But problem is, if you have ign + and earthed temp sensor on the coil side, then turn ignition off, the switching side of the relay connects and the fan turns on??
It seems like you always need power across the coil to keep it from connecting?
Or what you say about the common terminal getting power from another relay triggered by ign + , does this solve it?
Thanks
Joel
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: 4AGE thermo fan switch wiring
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Sat, 13 November 2004 06:06
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yup, the power to the load side of the relay must be provided by a a source that is triggered/supplied by IGN. otherwise, as you say, it will always be on when sensor is cold.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: 4AGE thermo fan switch wiring
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Sat, 13 November 2004 10:16
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oh forgot to mention...
i have same issue as you for thermo switch, but i also want a manual override switch in the cabin to turn thermo on..
i have a normally wired (ie normally closed) relay that has.
power from battery to fuse to in on power side of relay (30).
other power side (87) goes to thermo, which then has earth straight to battery.
for switching, i have relay coil power (85) coming from 'main/EFI' relay, then the earth side of the relay coil (86) is what turns it on and off..
in cabin, i have a switch that manually grounds the relay coil..
for the temp switch, which is NC, then open when hot, i was going to get a mini relay (since it only drives the other relay) that is SPDT...
power from 'main' relay (so it's only on with ign) goes to the relay coil in (85).
the coil is then grounded by the temp switch when cold, and this opens the normally closed/SPDT contact... (with the SPDT, you can easily switch around anyway...)
the grounding side of the 'thermofan relay' goes to the power in (30), and the switched side goes to earth.
so.. when the second relay is not energised (at high temp) it's contacts close and provide a grounding path for the first relay, causing fan to go on.
when temp decreases, and the temp switch closes, the second relay energises and opens the first relays grounding circuit...
i was thinking of using a SY-4066, but pretty much anything would work.. a solid state one you could tape up would be nice..
Cya, Stewart
ps something like this
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Location:
Terrigal
Registered:
May 2002
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Re: 4AGE thermo fan switch wiring
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Sat, 13 November 2004 20:36
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Thanks very much guys for the info! It is all clear to me now 
Its annoying things like this that after you hear the answer you think, I should have known that!
Anyhows.. Much appriciated
Cheers
Joel
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