rad fan re-wiring assistance

dark_knight

Member +
trip wire

so Stu-, it so happens that this didn't quite work as i'd have imagined. i unplugged the thermo switch at the stat housing and nothing. ignition was on but engine off -- i just wanted to test the theory. will try again with the engine running but i doubt this will change anything..
 

dark_knight

Member +
wire plan

i then decided to do some further research. the wire leading to the thermo switch carries 12+ vdc juice that is ignition controlled (offline when the key is at 'off').. so this makes my work even easier. will just add a tri-pole switch in-between as shown in this schematic and extend the wires into the cabin. depending on which switch i'll get -- whether the on/auto parking pole switch on the right side of the steering, or the boost hi/lo/hazard/defrost switch that reside on the centre console -- i'll then decide how long to pull the wires..
this will work a treat given that it's been so hot of late.. i'm sure the engine will be happier.. :)

i'm under the assumption that the thermo-switch-to-rad-fan-relay wiring is only within the engine bay (thermo switch to fuse box) and does not get into the cabin at any point. can anyone confirm this..?
 
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Texx

Super Moderator
now, if only Texx would share a schematic of his explanation above.. :D

For some reason I was unsubscribed from this thread so didn't notice the replies.



so Stu-, it so happens that this didn't quite work as i'd have imagined. i unplugged the thermo switch at the stat housing and nothing. ignition was on but engine off -- i just wanted to test the theory. will try again with the engine running but i doubt this will change anything..

i then decided to do some further research. the wire leading to the thermo switch carries 12+ vdc juice that is ignition controlled (offline when the key is at 'off').. so this makes my work even easier. will just add a tri-pole switch in-between as shown in this schematic and extend the wires into the cabin. depending on which switch i'll get -- whether the on/auto parking pole switch on the right side of the steering, or the boost hi/lo/hazard/defrost switch that reside on the centre console -- i'll then decide how long to pull the wires..
this will work a treat given that it's been so hot of late.. i'm sure the engine will be happier.. :)

i'm under the assumption that the thermo-switch-to-rad-fan-relay wiring is only within the engine bay (thermo switch to fuse box) and does not get into the cabin at any point. can anyone confirm this..?



With your everyday typical relay (normally open) the switch contacts are open until the coil side is energised, the electromagnetic field created by the coil pulls the switch contacts together switching ON the circuit that the relay controls.

The rad fan relay is slightly different, it's a normally closed relay. The switch contacts are closed until the coil side is energised, the electromagnetic field created by the coil pulls the switch contacts apart switching OFF the circuit that the relay controls.

The rad fan thermo switch is connected between body ground and the coil ground terminal of the rad fan relay, it's a positive temperature coefficient switch which simply means that as it heats up it's electrical resistance increases to the point it gives infinite resistance or open circuit if you like.

Assuming all the relevant wiring and components are working correctly, with the ignition on and the engine coolant cold, the thermo switch is closed and earthing the ground terminal of the rad fan relay. This causes the normally closed relay switch contacts to open and the rad fan to turn OFF. When the coolant temperature increases above the thermo switch rating or the connection between the thermo switch and ground terminal of the rad fan relay is broken, the relay switch contacts return to their normally closed position and the rad fan is switched ON.


If you connect your switch as shown in your diagram and switch the +12v at the thermo switch to ground, the contacts in the rad fan relay will be switched open and the rad fan will never switch ON.
 

dark_knight

Member +
sense

thanks Texx for your very detailed explanation on this, however, (i think) i have a slightly different experience with this. earlier on today, i went tinkering around the bay and when i ground the thermo-switch plug, the rad fan comes to life (with IGN on). this leads me to think that the thermo-switch is a NO (normally open) switch when cold and as it heats up, resistance drops to near zero which then completes the relay circuit and triggers the rad fan.

now i know everything i'm saying is the direct opposite of what you have just explained.. but this is something i did practically. is it possible that your got your explanation(s) right but only swapped your 'open' & 'closed' definitions..?
 

weeJohn

Lifer
The fact the rad fan comes on when you remove the plug from the switch explains it. There is no possible power to earth circuit on the relay coil when the plug is removed so the relay must be normally closed for the system to work. The switch is closed when the engine is cold, which energises the relay and opens the contacts that power the rad fan, when the engine gets up to temp the switch opens, powers down the relay coil and closes the before opened contacts for rad fan power.

Its a fail safe system, if there is a problem with the wiring to the switch or plug, it means the fan runs. Only a sticky switch will make it not come on.
 

Texx

Super Moderator
thanks Texx for your very detailed explanation on this, however, (i think) i have a slightly different experience with this. earlier on today, i went tinkering around the bay and when i ground the thermo-switch plug, the rad fan comes to life (with IGN on). this leads me to think that the thermo-switch is a NO (normally open) switch when cold and as it heats up, resistance drops to near zero which then completes the relay circuit and triggers the rad fan.

now i know everything i'm saying is the direct opposite of what you have just explained.. but this is something i did practically. is it possible that your got your explanation(s) right but only swapped your 'open' & 'closed' definitions..?


I'm struggling to find an explanation for what you've discovered, maybe the EP91 circuit works differently? I've checked through several other Toyota circuit diagrams (SW20 MR2, EL51/53 Tercel, ST205 Celica, AE111 Corolla, MCV21W Camry) and they all appear to work in a similar way i.e. a PTC thermo switch and NC relay.
 

dark_knight

Member +
baffled

it also baffles me Texx.. and like weeJohn also mentioned, what you explained is also what i'd expect to see in order to make the electrics fail-safe in case of thermo switch failure. my glanza p-sport platform shouldn't be any different, or so i'd like to believe..

in my case, my thermo switch wire is energized (with IGN on) -- so i'm guessing this line is from the rad fan relay 1. when hot, my thermo switch then makes contact (to ground) which then triggers the relay to power the rad fan. i used this very same schematic to add the override switch and it works perfectly. temps drop all the way to thermostatic levels which is around 84 deg C -- very helpful in our sweltering heat wave season & slow traffic.. :)
 

weeJohn

Lifer
You have to remember its a DC circuit you are dealing with, the circuit does not conduct any current until it is completed, ie, one end is connected to positive and the other negative. Current is what makes the circuit operate, to make current you need to have voltage passing from positive to negative through a resistance. In this case the resistance is the coil of the relay, the voltage will be able to be read all the way through the circuit from positive, including through any coil or closed switch, until it comes to a piece that breaks the circuit. At that point, the other side of the break is connected to the negative so it does not have any voltage. When the break in the circuit is closed then current flows and the coil gets energised, you can have 500 volts DC flowing through that coil and out the wire to the switch, it wont energise the coil until the circuit is completed to negative.

After saying all this but, I do remember when I did my first EP91 turbo conversion, the rad fan would not switch on. I thought the switch in the EP82 engine I had fitted was faulty, so I switched it for the one from the original EP91 engine. There is a possibility that the circuit is wired differently, but if you take the plug off and the fan runs, then its wired as described with a normally closed relay.
 
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weeJohn

Lifer
Take the rad fan relay out of the fuse box, measure for resistance on the 2 pins that are opposite to each other. You should have 0 Ohms across 2 and a resistance (I will guess 600 Ohms lol) across the other 2. If so, its a normally closed relay, if you have only a high resistance across 1 pair, then Texx and I are dicks lol.
 

dark_knight

Member +
rad fan relay 1

weeJohn, despite it being a chilly night, as soon as i read your response, i left in my boxers only, popped my hood, took out the relay and took the readings just to certify that i'm not going nuts on this.. :)

here's my simple response -- i do better with pictures.. you know what they say; 1 pic = 1,000 words. :)
 

Texx

Super Moderator
In that case I can only assume the rad fan relay in an EP91 Glanza is controlled by the A/C ECU. If you pull the connector from the A/C gas pressure switch I'll take a guess and say the fan doesn't fun continuously with the A/C OFF like it would with an EP82?
 

dark_knight

Member +
platform differences

damn straight Texx. i gutted my air-con not-so-recently and didn't have to do the pressure switch bridging that i've seen people talk of on the forum in order to keep the rad fan from constantly running. so, on my platform, unplugging the air-con pressure switch or the thermo-switch does not trigger the rad fan. i guess that's the primary difference here..
 

weeJohn

Lifer
Every day is a school day, you learn something if your eyes are open.

Thats the problem with helping out sometimes, you end up being wrong!

Maybe you can trace the relay wires dark_knight and see where they go, it would be good to know.

Going back to the original thread topic, if you wire a switch in so that when the contacts are open it will break the rad fan switch wires and closed it will continue the circuit, you will have auto/manual control.
 

dark_knight

Member +
school all day every day

hehe weeJohn.. you're right. everyday is a school day, even for me.. :)
i will trace the wires later, although i think they just run from the switch to the relay and relay to rad fan since it's an exclusive circuit and not ecu-related. as it is right now, my wiring is exactly like i had already shared here. the override grounds the relay trigger which runs the fan, on switching back to 'auto', it waits to read from the thermo switch.

i guess this kinda hints to me that lots of you UK folk have GTs and not glanzas huh..? :D
 

bender

Member +
Every day is a school day, you learn something if your eyes are open.

Thats the problem with helping out sometimes, you end up being wrong!

Maybe you can trace the relay wires dark_knight and see where they go, it would be good to know.

Going back to the original thread topic, if you wire a switch in so that when the contacts are open it will break the rad fan switch wires and closed it will continue the circuit, you will have auto/manual control.
did you guys figure out where these wires go? i have a glanza V and am trouble shooting my fan not running, the fan will run when i turn the AC on but i dont believe it is coming on when engine reaches operating temp, does the fan always kick in on your drive or only in the sweltering heat? My guess is the relay or the temp sensor is bad
 

Jay

Admin
It'll take a long time at idling from cold before you hear the fan come into play in my experience. Probably around 15 mins depending on ambient temp. A long hot run would help work out if there's an issue, note it only kicks on for short bursts too.

Will try to hoke out the testing procedure later from the manuals.

If there's a break in the fan switch wiring the fan will just run constant so you can rule that out at least.

EDIT - Bollocks, just realised you're talking about the glanza version, my bad! In that case I might not have the books and your wiring doesn't have the failsafe. I should have read the thread. Let me have a look later at what I can find.
 
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bender

Member +
It'll take a long time at idling from cold before you hear the fan come into play in my experience. Probably around 15 mins depending on ambient temp. A long hot run would help work out if there's an issue, note it only kicks on for short bursts too.

Will try to hoke out the testing procedure later from the manuals.

If there's a break in the fan switch wiring the fan will just run constant so you can rule that out at least.

EDIT - Bollocks, just realised you're talking about the glanza version, my bad! In that case I might not have the books and your wiring doesn't have the failsafe. I should have read the thread. Let me have a look later at what I can find.
Thanks, yeah my glanzas fan will turn on with the AC on, so the fan itself works, ive ordered a new cooling fan sensor, is there a way i can test this sensor in the meantime?
 

Jay

Admin
I checked the ep82 and paseo manuals this morning, unfortunately they are the earlier system but I've attached the test instructions in case you can adapt them to suit.

(Right click, save, rotate and stick them in page order as the upload function has a mind of its own!)
 

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Jay

Admin
With regards to your fan, unplug it and manually check that the motor is turning freely with no resistance. As you mentioned it might be feeling its age after all these years.
 
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