hiya

trying to work out why my rad fan isn't coming on

I have the carb version of the Ford 2.0 DOHC - approx 1990, with a basic engine management system

there is a sensor on the thermostat housing (or thereabouts) which has 4 wires:

2 x black - joined together and connected to what I think is the E/M module power relay

Black/Red - goes to the fan connection block, but no further

Black/Blue goes to the fan.

The fan has a seperate earth

I'm guessing that the power comes from the relay and the sensor switches it through to the fan - is that right?

any clues as to how I can test it please?

cheers

Terry
Rescued attachment rad_fan_wiring.jpg

As standard the dohc sierra had two fans, it was very susceptable to head warpage and cracking through heat. The wire you show as not connected is for the second fan.

The two blacks should be live when the ignition is on, if they are not thats where your fault lies.

[Edited on 4/6/09 by r1_pete]

Surely the Thermostat should run across the input on the relay, and the fan connected direct to the output relay. After all, thats how a relay works.

Its seems your way has all the load going through the thermostat to supply the fan. I make no claims to being an electrical expert, but thats not how I'd wire it.

quote:

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Originally posted by deezee
Surely the Thermostat should run across the input on the relay, and the fan connected direct to the output relay. After all, thats how a relay works.

Its seems your way has all the load going through the thermostat to supply the fan. I make no claims to being an electrical expert, but thats not how I'd wire it.

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I thought there should be a relay too, but asked at got this: Linky

HTH
Chris

R1 pete is correct, the thermostat has 2 poles (switches) inside, one set to close at 85 degrees the other about 90 degrees. i.e two stage, you need 12v on blacks (relay energized) and then as temp rises thermostat contacts close

ta very much!

I had my suspiscions about 2 fans, but mine runs really cool - hardly used to get above cold on the original ford temp gauge, and the fan very rarely came on. I'll assume it's working for now and do a bit of testing after the MoT this afternoon.

can I wire in a manual switch (in case of emergencies) like this:

wire from black to switch
wire from fan to switch

so basically I bypass the fan sensor if I need to turn it on manually

cheers!
Rescued attachment rad_fan_wiring_with_switch.jpg