Failure modes of fridge thermostat?

Just had a failure and had to replace with a new thermostat/temp control

This is a gas operated thermostat that works a simple built in on/off microswitch, the knob is to set the switch temp. point. The gas bellows and capillary pipe is operating and undamaged. Age about 20 years. Mine failed in the fact that it wouldnt switch once in the off or on state.

For info pic. here:

Anyone know what fails in these units? Seems not much to go wrong as long as the gas parts are undamaged? Before I have to destructively disect it!! C+

After 20 years mechanical wear in the switching lever etc. leads to intermittent operation also the contacts can wear out as well.

Here's a cross section of the guts: I once took one apart, but didn't find anything profound.

My rule of thumb is "if it moves, it breaks". Therefore, the first things I suspect are the parts that move. My best guess(tm) is the arm that pushes the contacts, which moves every time the thermostat cycles[1]. When you tear it apart, look for wear. Also look for arced contacts.

[1] My fridge cycles about once every 15 minutes or 35,000 times per year. I would guess(tm) that the switch were good for 100,000 cycles or about 3 years.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

On Mon, 29 Jun 2015 08:03:19 -0700, Jeff Liebermann wrote as underneath :

Thanks, youv' been down this same curiosity route! My unit is completely different layout from your crossectional drawing. It has three (preset) adjustors but cant tell what they each do without disassembly. I couldnt find any exploded or technical drawing on the web. I think people would be pissed off if their fridges worked for only about 3 years! Here is the Mfg. sales blurb page for the unit in question for anyone who might be interested - Jeff I notice 200K cycles! C+

There is an over-center spring in the tyupical "microswitch". It is made from a single strip of phosphor-bronze spring material with some slots stamped in it. The middle strip bows and flips from one side to the other of the outer part of the strip, making it bistable. Either the contacts erode, or the spring develops fatigue. No sane way to repair them, but often the switch is a standard size and can be replaced, if a complete replacement unit can't be had.

Jon