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I'm wondering if a faulty thermostat is what is causing my fridge freezer to misbehave? The fridge gets down to 12C, and the freezer to -20C or so, then the compressor does nothing for hours and it comes back up to ambient-ish.

The fridge-freezer is a Hotpoint RFA52 The thermostat is a Danfoss 077B3281 B62 -20.0 -34.0,

I have taken the thermostat out to test continuity (results as follows), but not being sure of which pin is doing what, I've tested each pin against each other, at ambient and then with an ice block held against the temperature sensing tube.

Does this look like a faulty thermostat?

continuity test results: (/ohm, high = out of range)

resistance at ambient, to ground
setting    pin3    pin4    pin6
off        high    high    high
1          high    high    high
2          high    high    high
3          high    high    high
4          high    high    high
5          high    high    high

-

resistance at ambient, to pin 3
setting    pin4    pin6
off        0.5    high
1          0.5    0.5
2          0.5    0.5
3          0.5    0.5
4          0.5    0.5
5          0.5    0.5

-

resistance at ambient, to pin 4 
setting    pin6 
off        high
1          0.5
2          0.5
3          0.5
4          0.5
5          0.5

All results were the same when the temperature sensing tube was held against an ice block as well!

  • As well as main thermostat fridge-freezers often have defrost circuits with a defrost timer with motor and a defrost thermostat. It's possible that eg the defrost timer motor is dead or walking wounded and failing to restore operation when it should. Get a manual for the fridge taht shows cct diagram and try shorting contacts that are switched by timer based systems. Beware of course shorting mains to ground OR mains to you. – Russell McMahon Nov 30 '16 at 17:10
  • A block of ice may not be cold enough to fully test the thermostat if it is normally attached to the evaporator coil, however it looks like all the combinations of the thermostat are showing closed where power would be connected through the thermostat to the compressor. There are several other things that can cause intermittent temp cycling the defrost cycle is one of those as already suggested. Another possibility is an improper Freon charge due to a leak or moisture in the system that is freezing and blocking the capilary tube or throttling valve (txv) would be my first checks. – Ed Beal May 10 '17 at 3:06
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One sign that a freezer is not keeping a constant temperature is bad freezer burn (ice crystals forming around your food, dehydration, damage).

You could use an indoor/outdoor thermometer that records high/low in order to debug this. Each day, record the high/low then reset the thermometer.

If you are seeing a big range in temperature, or, your freezer is getting warm enough to start melting, then I would replace the thermostat.

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