12V To The Radiator Fans

[Tim Kay]

In an attempt to diagnose my Lucas radiator fans not operating I'm wondering this: There are two wires, black & red, coming off the fan. For testing purpose, I attached 12V power supply to the red wire and when I put a test light on the black wire I have 12V power there too. I'm assuming that's not right, is the fan defective?

I am going to do further test on the relay as well because I'm not getting power to the fans at all when connected to the proper plugs. Seems to me this power source issue may be related to the defective fans.

Tim

 

[Mike Pass]

The test you did is OK. The test light should light up if the fan windings are OK. The simplest thing is just to connect the fan direct to the battery. If the fan works then this is not the problem. If the fan does not run it's new fan time. If you connect the fan the wrong way round it should just run backwards.
If the fan is Ok your next port of call is the fuse box. Check the fuse that's switches the fan. Usually the fan will be run via a relay. This is done to keep the heavy fan current from passing through the switch which would give the switch contacts a hard life. The fan switch would only be used to send a low current supply to the fan relay. A thick wire would be connected to the relay to give the large current needed to drive the fans which would normally take about 10amps each. Find where your fuses are and where the fan relay is located if fitted. Use your test light to see which bits are live and trace the connections through.
Cheers
Mike

 

[Jack]

Key word, Lucas!

 

[Tim Kay]

Mike, You are correct. I was afraid to touch the black wire, being 'hot', in fear of making things worse. The fans are working fine now that I have put straight battery power to them. So on to the next, I'll check the relays (fuse is fine)

And Jack, you are right to. Lucas, the Prince of Darkness, is always my first suspect but falsely accused in this case!

Tim

 

[Mike Pass]

Apparently the trick with all Lucas equipment is to keep the smoke INSIDE the wires! Good luck with the wiring.
Cheers
Mike