Wiring of fan thermostat

[JohnFol]

I was expecting a simple "on off" bimetallic strip affair for activating the radiator fan, i.e. the switch opens or closes when the coolant is up to a certain temperature. Looks like there are 2 wire connections and a 3rd earthing (?) connector as part of the copper washer.

I'd like to test it whilst off the car but no longer sure what "good" looks like

[peteracs]

Hi John

From memory the two pins are the switch and the earth is for the radiator itself. So test across the two pins for open/closed at temperature. The reason for it is the fan is wired into the circuit and the earth is on the fan side not the switch. (This is from memory, so happy to be corrected...)

Peter

[WestonE]

Hi John

Do check if there are 2 temp numbers on the fan switch. If so you can choose the lower one to have your single fan switch in earlier. on cars in other markets there were 2 fans and they switch in at different temps. Car Builder Solutions can sell you new switches in the 22mm size required.

Eric 

[JohnFol]

Open circuit at room temperature and was wired in parallel with manual switch so I think the earth is a red herring but will be boiling up some water later (or blow torch might be quicker)

[mtulloch]

There are 3 wires from the stat on my VX, 1 long with spade connector goes to the earthing tree behind the drivers headlights. The short one with the bullet connector goes to the fan, possibly via a rely, I can't remember. The short wire with the spade connector goes to the copper washer.

[JohnFol]

So effectively 2 earth wires so I'd guess the fan is at 12v and earthed out via thermostat wired in series.

[peteracs]

Hi John

From memory the two pins are the switch and the earth is for the radiator itself. So test across the two pins for open/closed at temperature. The reason for it is the fan is wired into the circuit and the earth is on the fan side not the switch. (This is from memory, so happy to be corrected...)

Peter

I shall correct myself. As mentioned above according to the wiring diagram I have (Haynes pre f/l) the switch has one pin going to earth and the other going to the relay which powers the fan.

Peter

[JohnFol]

Thanks Peter.

FYI just did the "stick it in a kettle" test and although resistance drops it never gets to close the circuit. May as well get it replaced.

[peteracs]

Hi John

That sounds like a good idea, a lot cheaper than a cooked engine.

Peter

[SanRemo78]

I'm a firm believer in a second earth wire from the relay via a dash mounted switch to pre-empt the thermoswitch. The driver will know way in advance if the engine is going to get warm when sat in traffic!

[WestonE]

I am with you on the extra fan relay switch and have that already to go on my lower center console. As I am installing an ECU I will also have the ECU switching on the pair of fans relating to the temp at the top of the engine, a pair of green fans on lights and a nice new radiator temp switch in the radiator.

I have had the dreaded temp still climbing no fan switching in several times in my history of Beta ownership.