Cooling Fan Relay Box Cover

[Steve2016]

Having checked out the relays, I reassembled the electronics outside of the black box for another test.

I connected it up to the car and put the fuse back in - no fan!!

I did what you suggested - position II, Aircon off, select Demist - still no fan.

Is there a way to test the HIGH speed fan other than by getting up to temp?

As a final sanity check, I disconnected the big relay from the PCB and triggered it via a battery - the fan ran.

Maybe the PCB has got fed up and shut down completely, or maybe my fiddling has made it work properly and it is the resistor after all (probably wishful thinking, but sometimes connections just need to be moved to make proper contact - like batteries in a TV controller).

I will look at getting a new resistor and take it from there.

In the mean time I'll try to think of a work around, so I can get to work!

Many thanks to everyone for their help.

Life would be dull without stuff to fix.

[SD1too]

Originally Posted by Steve2016

... I disconnected the big relay from the PCB and triggered it via a battery - the fan ran.

Hi Steve,

By doing this you've proved that your fan motor is working on full speed.
If you do the same test with the small relay you will find out whether the circuit is continuous through the silver resistor. If it is, then the PCB has certainly failed.


Simon

[vitesse]

As Simon has suggested do the same trick with the smaller relay but at the moment we don't know if the silver resistor has failed.

I've never tried it but I would have though that if you bridge the resistor in/out wiring with cable and the fan then runs (at high speed) that would prove the resistor at fault (?).

Regards

[SD1too]

Originally Posted by vitesse

... I would have though that if you bridge the resistor in/out wiring with cable and the fan then runs (at high speed) that would prove the resistor at fault (?).

Yes that's correct Mike. If you do this Steve (1) make sure that your bridging wire is sufficiently thick to carry the current and (2) do it only for a few seconds as the small relay isn't rated for full speed running. If you have a multimeter you can check the resistor for continuity without any risk.

Simon

[Steve2016]

So, I bought a new resistor from DMGRS and fitted it - everything is working normally again !

Thanks for all the advice. If I hadn't received the resistor so quickly I would have tested the other relay as you suggested above.

I have to say that the job was not as onerous to do as I had expected; the front end actually comes off pretty easily (and went back on almost as easily). Like many things it is mostly about patience and perseverance - plus of course expert advice from those who know!

The main thing is I have solved another problem, learnt more things and it only cost me £16.

Thanks again everyone,
Steve

[Arctic]

Hi Steve.
Excellent news, i know you most likely have but did you make sure you added some good heat shrink to the ends of the gold resistor, as you did when you found the chaffing.
1

Also made sure that the wiring can no longer touch the condenser behind the fan.

[Steve2016]

Originally Posted by Arctic

Hi Steve.
Excellent news, i know you most likely have but did you make sure you added some good heat shrink to the ends of the gold resistor, as you did when you found the chaffing.
1

Also made sure that the wiring can no longer touch the condenser behind the fan.

Well, I didn't add heatshrink (TBH it never crossed my mind!), partly as I poked each wire end through the hole in the terminal, then soldered it in place, so this arrangement didn't really lend itself to heatshrinking.

The way I cut the wires, to remove any damaged areas, left very little free play and I also cable tied them to the frame, so no danger of them rubbing on anything.

Regards,
Steve

[Arctic]

Originally Posted by Steve2016

The way I cut the wires, to remove any damaged areas, left very little free play and I also cable tied them to the frame, so no danger of them rubbing on anything.

Regards,
Steve

Hi Steve.
You will have to keep an eye on the ends of the resistor, as corrosion could occur and it as the potential to blow the resistor, the ones i do are also soldered as well as using a connector.

[Steve2016]

Thanks for the Heads-up Arctic. I should have thought of that, but hey ho. I'll keep an eye on it. At least I know how to take it all apart now, for next time.

MOT next month, so could be the least of my worries... Nope, think positive!

[SD1too]

Originally Posted by Steve2016

... the insulation on the two wires to and from the resistor are both quite heavily chafed, by the look of it from rubbing on the radiator cooling fins ... it looks like at least one of them has exposed the metal wire inside. Could this be the cause of the problem ...

It's now apparent that this was probably responsible for your fan running continuously, even with the ignition key removed. The bare wires touching the radiator provided an earth path for the motor, by-passing the control box relays.

Well done Steve!

Simon