BX16V.com Forum

The good old BX fan question....

Can anyone help me out abit please! I have bridged the connector on the fan switch to trick the car into thinking the fans are on and measured the voltage that goes to the fan. mine is 12v but neither of the 2 fans i have fire up, although they do once connected straight to the battery???

It doesnt seem to matter which way round the resitor with no wire is or which pin is bridged on the switch plug. If i unplug the wire bridging the pins the voltage is 0v otherwise its 12v?

Whats your run at? please!

TIM

Hi Tim,

Firstly you need to check that you have 12 volts to the fan, since the fan sits in the 'live' side of the line. The thermo-switch does the switching to ground, whether through the resistor or not.

If you don't have 12V to the fan, check fuses 1 and 5. Then check control relay R1.

Hope this helps a little,
Cheers

I have 12v where the wires go to the fan.... I'm a little confused. where else should I check for voltage?

TIM

If the loom is standard then as said above, the fans are always live, they are switched through earth to fire 'em in. So if you've got 12v at the fans then check relay R1, try changing it, they are known to fail, and as above fuses 1 and 5. If all this checks out ok then it's dropped the earth

Cheers
Chris G

Tim,
You should also have 12V to the resistor and ultimately the thermo switch, since this acts as a ground switch. Also check resistance between the ground wire on the thermoswitch and a known good ground (probably straight back to the earth terminal of the battery).

I'm just wondering whether you are seeing 12v at the input side of the fan, but with no amperage driving it? So, you may want to run a wire between the ground side of the fans and the battery earth, thus eliminating the resistor and thermoswitch completely. If you have a good 12v supply, then the fans should fire up.

Let us know how you get on.
Cheers

not sure i fully understand but will have a play with the multimeter tomorrow after work and see what happens. I'm a little confused that the fan can have 12v but not go!?
I have checked all the fuses but where is R1 relay? first one on the left in the box under the glove box?
I hate BX fans! why couldnt I find one with working fans!

TIM

Tim2cv wrote:I'm a little confused that the fan can have 12v but not go!?

As far as I can work out Tim - I'm no electrician but... sounds like the fans always have +12v fed to them, but the thermoswitch connects the "other side" of the fan to the -ve end of the circuit, completing the loop - so there's always +12v connected to the + side of the fan, but the circuit isn't complete until the thermoswitch has kicked in and connected the -ve end of the loop.

So I guess when you're testing the voltage at the fans that you have the negative end of your multimeter stuck on the -ve terminal on the battery or some such. If you tested across where the fan itself actually goes you would see no voltage.

with the thermo switch plug un-plugged and not bridged...



where are all the electrical geniouses? I dont want to have to re-wire this valver too!

TIM

the thermo switch has three terminals.

One is chassis 0V.

another is Fan via the low speed resistor.

another is fan directly.

If you short each pin to chassis:
one will do nothing,
one will give low speed fan,
the other will give high speed fan.

If all is OK.

One end of the fan will always have +12V with ignition on, but you will only measure this with the meter return lead to chassis.
Across the fan will be 0V, until the switch is closed.

Mike

Hi guys
While we are the subject of fans,how do I wire up two?
I've got them fitted and need to connect up.
Thanks