"Pat Coghlan" wrote in message
...
Don Young wrote:
"Pat Coghlan" wrote in message
...

It turns out there's a breaker/reset on the motor (mounted beside one of
the capacitors) which must have popped. My 7 year-old twin looked it
over and found it (well, I helped by turning it on its back in our
living room). There's no reference to it in the manual.

BTW, there's some kind of spring plunger on the side of the pressure
switch housing. I can't figure out what it does. If anything, it would
push *down* on the plate that rises to open the contacts (i.e. prevent
it from rising...but I don't see why anything would want to prevent
contacts from opening).


It may be an unloader valve which opens when the contacts open so that
the pressure in the compressor is released. This keeps the compressor
from trying to start with pressure in the cylinder(s).
It's similar to http://web.ncf.ca/ff293/Public/Switch.png (see red arrow)

When the little tab - which is part of the plate that moves the contacts -
below the brass cylinder (connected to tank pressure) rises, the contacts
open. The needle in the cylinder just sits there, with the tab rising to
meet it. If the needle were to get pushed down (from air pressure), this
would force the contacts to close and activate the motor. Why would the
designer want the motor to operate when pressure rises?
He wouldn't. The needle doesn't push the tab down, the tab pushes the needle
up when the contacts open to stop the compressor. This releases the pressure
in the compressor while a check valve holds pressure in the tank. When the
tank pressure drops, a diaphragm in the switch closes the contacts to start
the compressor. At the same time the needle is released so that the
compressor air is no longer vented and can build up pressure to open the
check valve and repressurize the tank.

Don Young