Fridge diagnostics with HE and $20 worth of Zigbee devices

We had a cold-freezer-warm-fridge situation which required immediate intervention. Taking off the freezer back panel revealed not only the evaporator completely frosted over but also the coil inlet and defrost thermostat completely encased in solid ice.

I did the obvious thing and defrosted everything. Next question is : what went wrong ? Is the defrost heater broken? (read 30 Ohms on the multimeter so should be good) Is the bimetal defrost thermostat defective? (would have to take the evaporator fan assembly apart to get to the leads so... dunno) Has the control board gone bad?

I decided to put the fridge back online, but this time connected through one of those slightly chatty Thirdreality energy-monitoring plugs and with a Sonoff temp sensor thrown in a ziploc bag, both of them hooked up to Grafana via the InfluxDB Logger app, so I could see what's going on.

The result :

Nice compressor startup spikes :slight_smile: So it's pretty clear the compressor is getting cycled as expected. Not sure what the short little spikes are... damper door? evap fan? Fridge was open a bit long around 1pm when my spouse loaded it with food, so temp went up. Otherwise seems like temp control is working OK (the SNZB-02 is not exactly a precise instrument).

Finally the event I was actually looking for occurred at 3:30pm : compressor turns off, then a 480W load for 10 min., then compressor turns back on. Sure looks like that 30 Ohm defrost heater is getting juice.

Pretty cool I was able to confirm everything is working as it should using $20 worth of stuff I had in a drawer. What went wrong? The only thing I haven't ruled out yet is the sealed system,

(someone later remembered the freezer door "might" have been left a open a crack for a "little" while)


That is why I have a Hue motion sensor in a ziplock back in my fridge's freezer. It's a triple threat with motion, temp, and lux. You can get ahead of temp rise by a timed lux notification.

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Good stuff. I keep my fridge on one of those so I can track historical usage after a similar issue with a sealed system failure.

Have you checked that the fans run? Are the condenser coils clean? If those are good I'm pretty certain it's the sealed system


That’s what I would check.

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I have temp/humidity sensors in the fridge/freezer and the snake food freezer which trip a Google routine to tell me to check the function of whichever one.. It trips after the sensor temp climbs over a certain point. Seems to work well. Surprised my carer today anyway.. I got some WiFi tuya T/H sensors spares so I used them for that purpose... Surprised how well they're working.

Does anyone know a way of dehumidifying the inside of a freezer because my fridge/freezer has a fetish for icing itself up solid.. I've tried the chemical evaporative types and they're useless...

Yes, both evaporator and condenser fans running.

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Do you have any water running into the evaporator pan at the bottom of the fridge? If the drain tube from the freezer to the evap pan is blocked, the defrosted ice (water) will remain in the freezer, were it will refreeze, and continuously increase in thickness.


Thanks. The drain is working fine. What you are describing is in fact a pretty common problem on this model and was fixed on this unit a few years in. Typically the accumulated water will drip down to the bottom of the freezer where it will ice up in an ever thickening sheet.

If this were an automotive air conditioner, I would say if everything is working correctly, the refrigerant charge is a tad low.

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Yeah, they can leak down over time since the pipes are slightly porous to the fluids/gases concerned.

Iirc the newer the coolant the more they leak/ooze (thus negating the whole bloody point, but hey).

It might also be worth checking metal fittings for corrosion just in case, because that can cause micro leaks.

I don't know about your fridge, but most have a defrost timer. Might google your model to see if it has one, and where it is.

I do similar, graphing power but just a temp/motion sensor in the fridge part. Do the same for my chest freezer. The power graph over time definitely will help show something is out of whack.

The temp sensor has a rule, to send a message to both of our cell phones to check the fridge.

FWIW, I'm using the OG Iris motion sensor that does temp/humidity. No plastic bag. Been in there for years and still going strong.


I've Tuya zigbee sensors in the fridge/freezer and the freezer for the snakes food. They seem to transmit fine but the batteries don't last very long, due to cold.
Have an alert through Google mini if the temps climb.

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Try covering the sensor with Scotch Tape.
It's my assumption (don't know if it's true or not), that encasing the sensor in scotch tape significantly increases battery life.
Another (or additional) way to lengthen battery life: put a (wired) repeater very close to the sensor (in direct line of sight).

No problems getting Zigbee out of the freezer?

Someone needs to tell Edward Snowden. He is big on putting cell phones in the freezer to prevent government snooping.

No Problem getting zigbee out of a freezer.
(Although the models with just a sensor probe that goes into the freezer, is probably preferred).

I even have one device, in a cold storage room with a sliding metal door.
Around once a day, the door opens, and I guess that's enough.

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Download the Hubitat app