Technical Cooling fans ... again.

[le cloropois]

Hoping someone can help!
Son has a 1985 Ducato 2.5 motorhome.
He bought the van last September, drove it 200 miles home to west Wales, then back up to Derbyshire, back to Wales again and down to Newhaven, for the ferry to Dieppe. Another 250 miles to us in France.
Just after purchase he had a garage-owning friend check it out, fix a few bits & mot.
Fans appeared not to work at all.
Mechanic friend decided on the emergency direct wiring of the fans, via a relay, to a 3-position switch, to switch them on if & when needed.
All worked fine on the couple of times sitting in traffic jams on M1 etc...
Parked up over winter, running engine once a week.
Last week the relay packed up, after several fuses blown. Replaced relay with new.
NOW, fans work ok when switched on, until after about a minute the fuse starts to bend visibly then blow.
Both fans appear to spin freely when turned by hand.
They continue to spin at full speed until the fuses blow, so not visibly seizing!

He's tidied up any frayed wires, cleaned all contacts, replaced relay, checked all wiring for shorts & cleaned fuse sockets etc.etc.

Beginning to run out of ideas!!

Thanks for any suggestions - apart from the obvious!! :bang:

 

[corcai]

What size is the fuse 30A in most vehicles, the fans would normally only operate for a minute or two, they may be binding in their bushes with expansion from heat over a long period of time.

 

[le cloropois]

Hi. Thanks for replying! 25a fuses were fitted when he bought the van. With 30a relays. They were working fine when needed (occasionally in heavy traffic etc). Only recently, the horn stopped working (replacement works fine so far) and the engine would only stop when sidelights switch pressed! Van's been parked up since october but regularly started & run, weekly. Time's been spent checking all wiring, contacts etc., then this fan fuse thing happened... Put new 40a relays & 30a fuses in - both fans work but fuses still blow after about a minute. The fans still turn freely by hand after the fuses blow, so don't appear to be seizing. Just re-read - shouldn't the fuse amps match the relay amps??

 

[CDK]

Only one way to find out: get a multimeter and measure the current running through each fan.
The typical current is 8-10 Amps, the inrush current will be higher but lasts less than 0.5 sec.
With fans over 30 years old the armature may have developed a temperature dependent short.
If the current is within range, check the connector the fuse is installed in. There may be corrosion there causing a higher contact resistance.

 

[le cloropois]

Thanks - good idea

 

[le cloropois]

SUSSED.

There seemed to be no reason for the fusus blowing as apart from cleaning all earths & other connections nothing had been altered from when the fans were working ok...

WE watched the fuses closely when the fans were switched on and noticed the plastic body of the fuses would start to soften, allowing the metal part to 'shrink', loosening the contact and allowing high resistance.

Put the 2 original fuses back in & all works fine.

Son had bought a box of assorted fuses off ebay. They are copies of proper fuses, with 'polythene' type bodies. The old originals are ceramic, as they're supposed to be, obviously.

Seemples - lateral thinking usually works .......................

 

[corcai]

SUSSED.

There seemed to be no reason for the fusus blowing as apart from cleaning all earths & other connections nothing had been altered from when the fans were working ok...

WE watched the fuses closely when the fans were switched on and noticed the plastic body of the fuses would start to soften, allowing the metal part to 'shrink', loosening the contact and allowing high resistance.

Put the 2 original fuses back in & all works fine.

Son had bought a box of assorted fuses off ebay. They are copies of proper fuses, with 'polythene' type bodies. The old originals are ceramic, as they're supposed to be, obviously.

Seemples - lateral thinking usually works .......................

lol thats a good one, chinese crap strikes again.