Thermostats

[davelowe]

Hi - my first post. I have a two year old very simple Currys Essentials under counter fridge. It is just a fridge and has no icebox nor is it combined with a freezer. It is running continuously and freezing things. I inspected the door seal which is perfect and there is no excessive moisture in the fridge. I looked at the wiring diagram and this has only three components - a thermostat, a compressor (with integral fan), and a light. There is no defrost heater or anything like that. The light goes out when the door closes. I removed the thermostat (and its built in capillary tube) and put my multimeter across the terminals to test it. It shows continuity regardless of the dial position. It only goes open circuit when the on off portion of the dial is in the off position. I put the thermostat in my freezer for two hours and then repeated the measurements: no change. I suspected it as having a fault (most likely welded contacts) so I ordered a replacement. I repeated these tests with the replacement but this showed the same behaviour. I ordered another replacement and this also seems faulty in the same way WTF(!)
Am I losing my mind or am I being VERY unlucky?!
Thanks for any help.

[Brian_UK]

It depends n the type of thermometer used.

On most the thermostat capillary when fitted makes contact with the "cold" refrigerant pipework to sense the temperature. You would be unlikely to be able to test it outside of the fridge.

Silly question but have you tried the new 'stat in the fridge ?

Please do check the thermostat type number of the replacements with the original. Some manufacturers have slight differences from off the shelf ones. Where did you get the replacements from?

[davelowe]

Hi Brian - yes I tested it in the fridge. It's been in for around 24 hrs and still running continuously. I have (two) thermometers in there to monitor the temperature - it hovers around the 0 - 1C mark. I haven't tested the second replacement one in there though - just had that in the freezer (ie -18C) for several hours. It was easier to test it like that than fit it.
I obtained the first replacement from an ebay seller with 10,000+ sales. It is branded (seems legit). The second replacement came from partmaster.co.uk (ie they are two different suppliers).
I assume that they should definitely shut off if exposed to -18C temps?
Thanks.
edit: the first replacement was an IDENTICAL part code; the second was a recommended alternative.

[redroge]

Does the back wall of the fridge frost up and is it frosting where the capillary is attached, is the capillary clamped to the back wall or is it in a socket.
If it is not frosting where the capillary is it could be slightly short of gas.

[davelowe]

Hi redroge - the capillary is in a socket (by which I mean it slides in a sleeve which is out of sight - it disappears from view behind where the thermostat mounts). I assume this sleeve leads it to the 'cold' pipework. The back of the fridge frosts up. It has no problem cooling. In fact it's too keen!
Thanks.

[redroge]

Could be the socket is not making good contact with the pipe work

[davelowe]

Hi redroge - I'm hoping that isn't the case because it would mean moving the integrated fridge out to get at the back of the thing :-(
Also, that wouldn't explain why the thermostats will not trip off when I put them in the freezer for hours (I don't think). But... it does seem a bit likely that you're right. I'm going to take the capillary out and shove it back in again to see if that seats it properly. Otherwise the siliconed in plinth etc will need to come out.
Thanks.

[Jeff Winsor]

On my own R600 fridge the cause was shortage of gas as all the evaporator plate was not being fed, especially the piece where the capillary was attached so did not get low enough temp to turn off.

[Glenn Moore]

Domestic thermostats normally use a simple capillary tube as the sensing element . But for the sensing element to work correctly the last 100mm/4inches of the capillary tube must be in contact with the evaporator plate.
Where a sensor tube or sleeve is embedded in the cabinet insulation ,the sleeve is attached to the suction end of the evaporator plate. So it is important that the sensor is pushed into the sleeve as far as possible for the sensor to operate correctly.
In fridges and freezers where the stat is inside the fridge the sensor is clamped onto the evaporator plate with a small plate .The end of the capillary is bent into a hairpin bend so that the end 100mm is in contact with the Evap.
Putting the stat into a freezer will not test the function of the stat.
You need a cold bath where you can put the end 100mm of the cap tube into the bath and then check the contacts to see if they open and close.
The old way of testing the stat was to spray liquid refrigerant onto the end of the cap tube sensor ,this would activate the contacts in a couple of seconds if it’s a functioning stat .

[nike123]

You are probably having problem of somewhat higher superheat at place where thermostat sensing element is in contact with evaporator, therefore your evaporator on that place never reaches cut-out temperature.
Cause for that could be refrigerant shortage, cappilary tube/filter-drier partial blockage, or bad thermal contact of thermostat bulb/tube to evaporator.

In this condition fridge still cools and ice is formed but not with full capacity.
Unfortunatly, these days, repair for that is usualy not economical except of last case.

In that case you can alternativly use air sensing thermostat to regulate temperature in refrigerator department.

https://www.amazon.co.uk/THERMOSTAT-PRODIGY-REFRIGERATOR-COLD-UNIVERSAL/dp/B00GPU49NI