CH compressor pressure switch died?

My slightly out-of-warranty (by 1 month) CH twin tank compressor won't switch on any more. I've hardly used the thing.
It has a LEFOO LF10-4H pressure switch which I suspect is the problem. I need to borrow a meter to check voltages at the contacts as a first step.
That said, is there some part that could have jammed that I could free somehow? There is a brass spring plunger on the side of the thing with a Torx adjustment screw (it touches the same plate that moves the contacts) whose function I don't really understand. I imagine there is also an assembly under the module that "pops up" to break the contacts when cut-out pressure is reached. This can be adjusted by two screws - one for both cut-in/cut-out pressure and one for cut-in only. I haven't changed these settings.
The damn switch costs more than half what I paid for the compressor!
Any info on what adjustments/checks I can do myself would be appreciated, especially a description of how the thing operates...including the plunger on the side.
I will also contact CH to see if they can do a warranty repair.
I'm not very impressed.
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The three adjustments are : Auto / OFF switch which should be set to Auto Setpoint which sets the Cut IN value Range which sets the differential and Cut out value Factory set Cut in 50psi Diff 30psi Cut out 80 psi

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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).
Telstra wrote:

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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).
Don Young
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Don Young wrote:

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?
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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
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Don Young wrote:

Ah, okay, that makes sense. I figured there must be something under the switch (diaphragm) moving the plate, but started to think that maybe the needle might be moving the contact plate, rather than as you described.
Does the diaphragm suddenly "pop up", opening the contacts and releasing pressure from the compressor? It would be hard to make the two happen gradually.
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