Non BX question

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Ian_Fearn
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Non BX question

Post by Ian_Fearn »

I've posted this on a VW forum but i'm expecting some more sensible answers from you chaps.....

I got my van last August and have been progressively sorting it out. In October i replaced the front to rear cooling pipes, rad, fan switch and thermostat.

Prior to me buying the van it had been fitted with a fan over-ride switch on the dash. I presumed this was because somebody didnt want to replace the fan switch. The wires for the switch seem pretty simple, they just piggyback onto the main feed for the fan from a relay under the dash and then another piggyback into the fuse box.

After all the work was done the fan still does not work if you leave it without manual intervention.

Today i tried to see why. If i bridge the terminals on the end of the connector at the rad end the fan works on both low and high speed.

How can i test to check the fan switch is actually working?

Cheers, Ian
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Post by jeremy »

To test the switch you need to get it to the switching temperature and see if it conducts. It may or may not be easy to get the thing to the correct temperature in the vehicle but what you need to do is to arrange to pass current through it and see if it starts to conduct when it reaches the cut-in temperature. It sounds as though this switch has 2 cut in's - and each must be checked. If I were doing it I'd remove the switch and put it in a saucepan of water on the stove with a thermometer. I'd connect a battery and indicator bulb (Draws nearly 2 amps at 12 volts - so tests the switch contacts thoroughly) into a circuit between the body or earth terminal and the section of the switch that I was testing - then cook and measure the temperature when the bulb lights. I'd also be looking to see that the bulb lights brightly - so that the contacts are good.

Its possible that the radiator is sludged and the switch doesn't get hot enough. A bypass switch is re-assuring if you are in traffic and start thoinking you've got a problem but obviously the thing should work properly on its own.
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Post by tom »

Switches get sluggish as they age. If it works at the connector, Ian, buy a new one because they can get so bad as to need 10 degrees extra by which time the engine is gone.
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Ian_Fearn
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Post by Ian_Fearn »

The frustation is that i fitted a new fan switch only 8 months ago. Is it possible i've got a dud?

The cooling systems on these are horrendous to bleed (engine at back, rad up front) so i'm trying to find a way of testing if the switch works before i swap it for another....
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Post by DLM »

The usual recommendation for testing a fan switch involves a saucepan, water, a hob, a thermometer to go in the pan (suspended, like the switch), and some form of continuity testing to the terminals on the switch - dependent on the form of switch. If you reach/exceed indicated temperature on the switch , and if you haven't got the continuity tester reporting, something is probably wrong. This may of course be the tester, or the contacts to/from it, though.....

I've never tried this, but others swear by it (and at it, possibly). remember that these switches (like the "just cooked" lamps on the BX dashboard) deteriorate with age, even if they're just sitting on the shelf, so a "new" switch may still have gone off calibrated temp.
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