Electric fan controller

[HealeyV8]

I have one of those "tadpole" type adjustable fan controllers where the probe goes into the top rad water hose. I fitted it ages ago and can't find the instructions. My car went in for some work and the garage hasn't put the wires back properly. As a make do I've by passed the controller and the fan runs all the time off ignition. I want to put it back properly this weekend but I'm stumped on why the controller switch has three connections, not just two.
I can't see any markings on the connections. Looking at the male spades it looks like the "spare" is on the right looking at the controller from the dial side.

Can anyone shed any light on what the third connection is for?

[GreenV8S]

Is it electrical or mechanical? If it's electrical, the third connection would be ground for the relay/transistor circuit (the others being permanent power in and switched power out).

If it's mechanical, I suppose it might have normally-open and normally-closed terminals (normally-closed not used in this application).

[HealeyV8]

Thanks GreenV8S, not sure it's very much like this

as you can see it's got three connections. I'd assumed one was power in and one power out when the temperature makes the connection.

[HealeyV8]

Actually I found another image


1. I assume is the live feed but what is 2 and C ?
I'm hoping mine is laid out the same but there are no markings I can see.

[Quinten]

That should help a little...

[GreenV8S]

That's a mechanical switch with one terminal normally-open and the other normally-closed. Hard to make out from the markings which is which.

Connect the Common terminal to the power supply. Connect terminal 1 to the fan positive. Ground the fan negative. If the fan runs when the engine is cold, move the fan connection from terminal 1 to terminal 2.

[E-bmw]

C - Common
2 - Normally closed (opens to break circuit with common on rise)
1 - Normally open (closes to make circuit with common on rise)

[HealeyV8]

Well that's confusing! Why put contacts 1 & 2 if one isn't used? Surely this must be for a purpose related to running a fan controlled by temperature?
The diagram looks like "common" goes to fan and 2 is live feed in.
GreenV8S is saying the other way around.

I assume I won't damage anything moving the connections around while trying to find the correct setup.
Really wish I could find the instructions for my actual switch.

[Quinten]

You can cause no harm if transposing any of the tabs, as long as you only feed a 12V into it (no ground!). The Common is called Common because it is either activated between 1 and C or activated between 2 and C. 1 or 2 should therefore normally be your "input", and C the "output".

[HealeyV8]

Quinten said:

You can cause no harm if transposing any of the tabs, as long as you only feed a 12V into it (no ground!). The Common is called Common because it is either activated between 1 and C or activated between 2 and C. 1 or 2 should therefore normally be your "input", and C the "output".

Thanks much appreciated

[200Plus Club]

Quinten said:

You can cause no harm if transposing any of the tabs, as long as you only feed a 12V into it (no ground!). The Common is called Common because it is either activated between 1 and C or activated between 2 and C. 1 or 2 should therefore normally be your "input", and C the "output".

OP- if you want to replace that unit with a much more modern and controllable unit, Davies Craig now supply digital fan controllers with a digital readout showing the actual set point and the water temperature. ive just fitted one to my Alfa, to control the rad fans. it will switch upto 30amp via onboard relay, and comes pre-wired. very easy fit, and very easy to set up, plus look a bit better than the older fashioned units. available in UK, this was the first pic I found of mine.

https://daviescraig.com.au/product/digital-thermat...

Edited by 200Plus Club on Tuesday 19th March 12:35

[GreenV8S]

HealeyV8 said:

Well that's confusing! Why put contacts 1 & 2 if one isn't used?

It's a generic industrial switch which could be used for many different applications. It can be used to switch things on when it gets hot, or switch things off. Here you want to switch the fan on when the engine is hot, so you will need to use the normally-closed normally-open terminal and the common terminal to complete that circuit.

Edited by GreenV8S on Tuesday 19th March 16:55

[E-bmw]

I think you meant normally open & common.

[Penelope Stopit]

http://www.farnell.com/datasheets/2052878.pdf?_ga=...

[GreenV8S]

E-bmw said:

I think you meant normally open & common.

You're right.

[anonymous-user]

HealeyV8 said:

Well that's confusing! Why put contacts 1 & 2 if one isn't used?

Because the thermostat is an off-the-shelf temperature switch used for a lot of different tasks, and they include normally open and normally closed contacts because they don't know if the end user of the thermal switch is "cooling" or "heating"! If you are cooling then you need to start (close the switch) the process when a certain temperature is reached, but if you are heating then you need to stop heating (ie OPEN the switch) when that temperature is reached!

[Penelope Stopit]

Max_Torque said:

HealeyV8 said:

Well that's confusing! Why put contacts 1 & 2 if one isn't used?

Because the thermostat is an off-the-shelf temperature switch used for a lot of different tasks, and they include normally open and normally closed contacts because they don't know if the end user of the thermal switch is "cooling" or "heating"! If you are cooling then you need to start (close the switch) the process when a certain temperature is reached, but if you are heating then you need to stop heating (ie OPEN the switch) when that temperature is reached!

When it is off off it is on and when it is on on it is off off
It can only be on off if it is off on
If it is on off with on on or on on with off on the contacts are welded

[HealeyV8]

Penelope Stopit said:

When it is off off it is on and when it is on on it is off off
It can only be on off if it is off on
If it is on off with on on or on on with off on the contacts are welded

You're messing with my melon, man!

[ruggedscotty]

Ok

Its a switch.

Its a temperature switch manufactured to change condition when a temperature value is met.

Switch manufacturer is thinking im making a switch for temperature, I can make one with two positions so that I can sell it to two markets, those that want something to happen with it gets hot and those that want something to happen when it gets cold.

The switch has a common connection. this is where the live normally goes. The two other contacts will connect to the common contact but not to each other, this means that when the temperature point set by the knob, the common connection will change over from one to the other, this giving you a change of state.


Hope that makes more sense.

[HealeyV8]

Thanks all got it all sorted this weekend. My switch had the legends 1 2 & 4 against the three contacts. So I assumed 1 was common and then followed the suggestion to find which post 2 or 4 worked for switching fan on when temperature reached.

Thanks guys for your help, much appreciated.