Low Speed Fan Not Working

[damien 22 1 Cars]

morning,

as above, my low speed fan isnt kicking in but the high speed is (when the engine gets super hot). ive bridged the brown plug and the low speed kicks in so i know the fan is ok, also have "borrowed" a known working temp switch (the one that sits in the rad) and it still dont come on.

being a simpltion im unsure on what to check next, any help would be great.

 

oh and if its any help when you turn the ignition on you can hear the high speed fan kick in for just a second then turn off.

 

thanks muchly

[blessed6383 0]

have you tryed changing the silver cylinder thing? has a brown plug connecting to it (forgot whats it called) it early should be under the battery or headlight its about the size of a finger and this has something to do with the fan speed i think

[Simes 248 2 Cars]

Taken from a post literally just below this one!

 

) Trouble-shooting thermoswitches and fans

 

Thermoswitches get old and fail. Fans can fail but I'd say it's rarer.

 

It's easier to test the fan really, by bridging the contacts on the thermoswitch. With the above explanation of how the switch itself works, it should be easy to see that by using a rubber/plastic/wooden handled screwdriver between pin 1 (12v live in) and pin 2 or 3, the fan should work. This DOES NOT test the switch itself.

 

If the fan does work then we know the fan's OK, but it should work on pin 2 (slow) and pin 3 (high). If it doesn't then the fan is likely knackered. If it works on one and not the other, it's likely to be a fault with the wiring going from the thermoswitch to the fan; it maybe a failed resistor.

 

If bridging pin 1 to 2 or 3 doesn't make the fan work, then test the fan in isolation, by taking 12v directly to the positive feed on the fan.

 

It's very difficult and fiddly to test thermoswitches, so I wouldn't bother. If the fan works in the test(s), then I'd just get a replacement thermoswitch.

[damien 22 1 Cars]

as said above, ive tested the fan and it works on both speeds, also tested the switch.

 

so that leaves the wiring and/or the resistor. is the resistor the "finger" thing? i know ive got 2 of them somewhere, off the top of my head one of them was something to do with the headlights?

[GLPoomobile 958]

Yes, it'll be your low speed resistor. The other resistor is the headlight dim/dip one.

 

If you pull the plug off it and bridge the contacts, the fan will come on at high speed when it gets to the lowest temp on the switch (i.e. when the fan would usually come on at the slow speed). That would prove it is the resistor at fault. I just discovered this problem with mine the other week, and I might just do away with the resistor and join the wires.

[MrG 3]

what does that do then GL, will the fan run continuously when the engine is running? I have a similar issue on mine and was thinking of dumping the fan for a kenlowe of sorts.

[blessed6383 0]

thats the thing (resistor) coldn't think of its name if you remove the resistor and bridge it, it will run at high speed instead of coming on at low speed then high so this is not a bad thing as it will be cooing it quicker in theory

[damien 22 1 Cars]

maybe cooling quicker but it will also overheat faster.

 

got it sorted, it was the resistor playing up

[GLPoomobile 958]

How's it going to overheat faster?

 

By removing/bypassing the slow speed resistor, all you are doing is making the fan come on at full speed at the point where it would normally come on at slow speed.

 

Let's say for example your rad switch is rated for the slow speed to kick in at 82 degrees. With the resistor bypassed, when you hit 82 degrees your fans come on at full speed instead, therefore bringing the temps back down quicker. In theory, they should stay on for a shorter duration than when on slow, as they should drop the temp back down to below 82 degrees quicker than if they were on at the slow speed.

 

Now if for some reason the temps continue to rise, once the switch gets to the 2nd temp rating where it would normally kick in the high speed fans, the fans will continue to run. all of this is being governed by the switch. The only purpose the resistor has in the whole scheme of things is to reduce the current to the fans so that they run at the slow speed when the switch dictates.

 

There's only 3 downsides that I can see to having no resistor

 

1 - noisey high speed fan more often

2 - accelerated wear to the fans due to only using high speed

3 - possible battery drain if your battery/alternator are in bad state

[damien 22 1 Cars]

How's it going to overheat faster?

 

By removing/bypassing the slow speed resistor, all you are doing is making the fan come on at full speed at the point where it would normally come on at slow speed.

 

ahh i see, this wasnt happening to me tho.

 

the engine temp was in the red to the point when the "stop" light came on then the high speed fan was kicking in.

 

i would of thought that without the low speed kicking in the engine temp would get too hot hence my thought the engine would overheat.

[GLPoomobile 958]

Yours did that because your resistor is bust, so you were getting no slow speed. Think about it - when the switch sees the lowest temp it sends current to the fans via the resistor, but if the resistor is bust, the fans don't get the current so don't come on. The temps keep climbing until the swicth gets to the next temp rating, and at that point it switches over so that the current goes down the other circuit that bypasses the resistor, and then the fans come on high speed.

 

In theory, it shouldn't be so hot that the stop light comes on before the high speed fans kick in. But that's exactly what mine did the other week. I'd refilled the coolant system and ran it up to temp whilst bleeding it, but the damn fans never cut in. I was watching the needle like a hawk, expecting them to come on at any second, and then the warning light and stop light came on. Weird thing is I'm sure it happened at a lower point on the gauge than I've had it before, and never had the warning lights come on!