Failure modes of fridge thermostat?

[Charlie+]

Just had a failure and had to replace with a new thermostat/temp control
(cost about Ł12), fridge now works fine again.
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:
https://www.dropbox.com/s/jxl1sd21cj7sqqb/Thermostat%20%28fridge%29.jpg?dl=0

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+

 

[Rheilly Phoull]

"Charlie+" wrote in message
news:i8u1papf90vqt5367esems36dvhphdl840@4ax.com...

Just had a failure and had to replace with a new thermostat/temp control
(cost about Ł12), fridge now works fine again.
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:
https://www.dropbox.com/s/jxl1sd21cj7sqqb/Thermostat%20%28fridge%29.jpg?dl=0

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.

 

[Jeff Liebermann]

On Mon, 29 Jun 2015 09:45:10 +0100, Charlie+ <charlie@xxx.net> wrote:

https://www.dropbox.com/s/jxl1sd21cj7sqqb/Thermostat%20%28fridge%29.jpg?dl=0

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+

Here's a cross section of the guts:
<http://appliancerepaircourses.com/wp-content/uploads/2013/09/Appliance-Correspondence-Course-Figure-1.52.jpg>
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

 

[Charlie+]

On Mon, 29 Jun 2015 08:03:19 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote as underneath :

On Mon, 29 Jun 2015 09:45:10 +0100, Charlie+ <charlie@xxx.net> wrote:

https://www.dropbox.com/s/jxl1sd21cj7sqqb/Thermostat%20%28fridge%29.jpg?dl=0

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+

Here's a cross section of the guts:
http://appliancerepaircourses.com/wp-content/uploads/2013/09/Appliance-Correspondence-Course-Figure-1.52.jpg
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.

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+
http://jjzh.en.alibaba.com/product/1863638984-213138937/K_series_Refrigerator_ranco_thermostat_k59.html

 

[Jon Elson]

Charlie+ wrote:

Just had a failure and had to replace with a new thermostat/temp control
(cost about ÂŁ12), fridge now works fine again.
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:

https://www.dropbox.com/s/jxl1sd21cj7sqqb/Thermostat%20%28fridge%29.jpg?dl=0

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+

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