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.