Jon Fairbairn wrote on 21/03/2009 :

So now I've got the covers off and have extracted a thing
that I'd expect to be a pressure switch,
http://www.cyberpieces.com/devis/pieces-detachees-lavage-sechage-g636-0.htm
has an image of something with the same part number.

My questions a

* is it actually just a pressure switch (on/off), or have
these things got more sophisticated since I last fiddled?

* would one expect to be able switch it by blowing into it?
I've tried, and while something clearly moves inside,
there's no click, and the resistance between pairs of
terminals remains the same (infinite for most pin
combinations, short circuit for one). This fits with my
hypothesis that it's running the pump until the pressure
switch says it's empty, and that never happens, but I
can't see how to refute it.

* given that it appears to have adjusting screws (one is
visible in the centre of the image at the above link, the
other is in the tube at the very front of the picture),
can I simply fit a replacement, or will I have to adjust
it up to fill to the right level? I don't have a service
manual, so I don't know the procedure.

That is just a pressure switch.

All those I have come across click when you suck/blow down the pipe,
though I suppose they might have conceivably have changed to a
capacitance type. Check the pipe is clear, they do block up other than
than it would be safe bet to get a replacement switch.

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk