Otter Switch for Fan

richardpope50 · Post by **richardpope50** » Mon Apr 04, 2011 5:28 pm

I have an otter switch in a swirl pot to switch on a fan at 96 degrees then off at 91 degrees - standard RV8 part. Despite this being a new one, my circuit is not working.

As the switch had two terminals I assumed it was an earth switch so when it reached 96 degrees it would eath (in may case, a fan relay) and fan turned on. However it doesn't. (My wiring circuit is OK, by the way.)

Do I assume I have misunderstood the wiring? If so, how should it be wired, please.

Post by **katanaman** » Mon Apr 04, 2011 5:35 pm

they are a straight switch as in when they make the two terminals are joined together. It could work the way you want but you will have to connect one terminal to earth and the other to the - of your relay coil or you could use it to switch the + to your relay as in battery-fuse-otter-from otter-relay +. Whichever way suits you best. Otter switches are capable of running a fan without a relay by the way but putting a relay in will help it last a bit longer.

richardpope50 · Post by **richardpope50** » Tue Apr 05, 2011 3:47 pm

katanaman wrote:...you will have to connect one terminal to earth and the other to the - of your relay coil ...

That's what I did but it does not work. This is the second switch. The first I checked in boiling water and it did not make a circuit between terminals so bought another one thinking it was duff. I have not tested the new one in water but it's not working either.

When I bypass the switch and connect the two terminals together the fan comes on.

I'm really puzzled.

richardpope50 · Post by **richardpope50** » Tue Apr 05, 2011 3:48 pm

katanaman wrote:...you will have to connect one terminal to earth and the other to the - of your relay coil ...

That's what I did but it does not work. This is the second switch. The first I checked in boiling water and it did not make a circuit between terminals so bought another one thinking it was duff. I have not tested the new one in water but it's not working either.

When I bypass the switch and connect the two terminals together the fan comes on.

I'm really puzzled.

Post by **katanaman** » Tue Apr 05, 2011 4:36 pm

Hmmm sounds like you need to check the new switch to be honest.

DEVONMAN · Post by **DEVONMAN** » Tue Apr 05, 2011 6:05 pm

Richard.
Don't know your layout but are you sure the switch is below the coolant level in the swirl pot. If not, the switch will not see the real temperature.

Regards Denis

Ian Anderson · Post by **Ian Anderson** » Tue Apr 05, 2011 6:26 pm

Where in your circuit is the switch located?

If it is in the section from engine to radiator switch is in water you should get the fans running

If it is from the outlet of the rad back to engine your switching temperature is too high. The water coming out the rad will be closer to 65 - 70 degrees on a good system.

I run a switch on the outlet of the radiator and used a ford part - cannot remember off hand which number but they have 3 set at different temperatures.

On the radiator outlet you will see less fluctuation in water temp and hence the fans will not switch on as often as on the engine outlet side.

Ian

ChrisJC · Post by **ChrisJC** » Tue Apr 05, 2011 6:54 pm

Is it rated highly enough to turn a fan on? The otter switch I am thinking of (which sits in the inlet manifold of a P6 just behind the thermostat) is for turning on the 'push in the choke' light, and would vapourise if you tried to switch 30Amps for an electric fan.....

Chris.

mgbv8 · Post by **mgbv8** » Tue Apr 05, 2011 8:03 pm

Richard!
Why would you use an otter switch in a swirl pot? This will surley see the sensing end seeing a mix of air and water?? Have I got that right??

As previously said, The otter switch is a pair of normally open contacts. So you can wire a + feed to the + side of the relay and wire the - side of the relay coil to one side of the otter switch with the other side going to earth which will close the relay. Or run the + feed to the otter switch to feed the + side of the relay to make it work as long as the - connection of the realy is grounded properly.

I ditched my otter switch and fitted an inline temp sensor in my top hose to trigger the fan relay on my MGB V8.

Are you sure the fans are working ok ??

Ian Anderson · Post by **Ian Anderson** » Tue Apr 05, 2011 9:07 pm

Last thought

Is the "circuit" made between one of the terminals and the houusing of the unit?

I you have used ptfe tape you may not have a good "earth"

Ian

Magnetteman · Post by **Magnetteman** » Fri Apr 15, 2011 4:43 pm

The swirl pot isn't mounted on rubber mounts is it?

That would be good enough to lose the earth connection.

Also, as MGBV8 said, why do you want a temp sensor in a swirl pot as it won't give a true water temperature reading?

richardpope50 · Post by **richardpope50** » Sat Apr 16, 2011 10:23 am

I've just seen that my long reply to you guys is not here. It was, I'm sure so sorry if you have not seen it.

Summary is that swirl pot from donor engine (TVR Griffiths) with Rover Otter switch in it. Plenty of water in swirl pot and circuit goes ign +ve to relay then relay -ve to Otter switch terminal then other terminal to bolted earth. When I bridge the two otter switch terminals, all works fine.

Otter switch is fitted using PTFE tape but swirl pot bolted direct to a chassis mounted plate so earth there.

My old Otter switch did not appear to work so got a replacement from Clevour Trevor as a TVR Griffiths stock part.

I'm going to have to check this new one in boiling water, I guess. Just got through IVA (see other post) so now chance to check things out.

I think my (TVR (CAI)) temp gauge is incorrectly showing temp. I'd got it to 105 degrees on dial but wondering how correct that is.

mgbv8 · Post by **mgbv8** » Sat Apr 16, 2011 10:37 pm

If you bridge the switch and all works then the internal conact isnt closing for some reason.

DEVONMAN · Post by **DEVONMAN** » Sun Apr 17, 2011 2:39 pm

mgbv8 wrote:If you bridge the switch and all works then the internal conact isnt closing for some reason.

Or, the engine is not actually getting up to switch on temperature.
You've not actualy said that the engine overheats, so maybe the gauge is just way inaccurate.
Regards Denis

spend · Post by **spend** » Sun Apr 17, 2011 5:13 pm

Just use an otter switch like the TVR, you will need to connect both of the spade terminals to complete a circuit.

Popular ones are Interpart 50250: 86-76C

The switch is in the bottom of the swirl tank & the tanks intended purpose is to separate air out of the coolant (mainly because the rad is relatively low)