fridge/freezer temperature regulation FAQ

A reasonably insulated and full freezer should take many hours to warm from -34C to -12C.

Freezer compartment is reasonably full, fridge less so (but does have quite a mass of drinks in it).

I have moved the thermometer around within the freezer compartment without resetting the min/max each time, so it could vary depending on proximity to the cooling coils which are mostly embedded within the shelves.

Keep in mind that the individual freezer contents won’t be swinging wildly in temperature, they will hover around the average.

Not cheap, but I use a SensorPush smart sensor (needs a free app) to monitor things like this. They have good accuracy (can be adjusted) but apart from the graphical displays of temperature and humidity, they also calculate and display the average (rather than the simple (high+low)/2), which gives a good estimate of the actual temperature of the freezer contents.

Are you sure that the LCD thermometer was giving a correct reading? Was it just the probe inside the freezer, and does it have a lowest use temperature stated? IMO -34°C is too low (I'm surprised a domestic freezer can get that low!). You're wasting energy and will probably get "freezer burn" with the extreme swings in temperature. I don't think that I've seen anything below -24°C with my FFFF.

Might be worth trying to get to the back of the unit and make sure that the heat exchanger is free of dust and other crud, and see if that affects the readings.

Ah, Those jabs really work. I have similar for statin replacement. Those jabs are evven more expensive.

I wouldn't think -34°C was possible to be honest. Heat pumps struggle to do more than about 40°C difference..

I get marked variations in frostiness with a full iced up freezing compartment ..

Certainly do, 22kg down since July.

I was a bit surprised at that one, I seem to remember lab-grade freezers being needed for that sort of temperature.

They look like an upmarket version of these:

The -20C lower limit might be a limitation for the OP (freezer should be -18C or lower). And humidity tends to under-read by about 10%. But they're only a few quid each and seem to last.

I can check them against other thermometers ...

Having had a look at the instruction leaflet, they only claim to read down to -20, supposed to display LL.L or HH.H when out of range ...

Exercise doesn't do much in the way of weight loss, unless it stops you eating so much of course.

Is there battery equipment (temperature monitor) in the freezer compartment and what type of battery are you using. An alkaline battery is only specified to around a -20C operating temperature. Freezer may go down to below this temperature. You need a lithium battery that is specified to around -40C

What type of LCD thermometer do you have. Some of the cheap ones are not specified much below 0C.

I have a wireless fridge/freezer thermometer identical to

When I first used them I used akaline batteries in the transmitters (which live in my fridge and freezer) but found the freezer side intermittent. They have been ultra reliable for the past 2+ years after I changed to lithium batteries in the transmitter sensors.

These

they're CR2032 coin cell powered, not sure how long the batteries will last in the freezer

thanks.

To check a freezer temperature something like

The thermometer in the freezer is reading -30 again

I've shoved a few 5kg iron weights in various trays, I'll let them chill down overnight, should get a pretty good reading off them with an IR thermometer (matt surface).

Yep, that's what I've done.

Remarkably, temperature across 4 devices of different makes is usually +/- 1C. It's humidity that is far less consistent.

Odd that they record -32C!

I've chucked one of those Thermopro things in the freezer middle drawer a few hours ago - seems to work fine, logging between -17 and -19C. The bluetooth range is (obviously) curtailed a fair bit, though. And it's got a lithium battery.

There can be good reasons for specifying equipment very conservatively. One example that I have been involved with is a network router that is specified down to 0 deg C (non condensing). In reality, when I tested a sample in my chest freezer on "boost" the temperature dropped to below

-30 deg C and the router worked fine from a cold startup. However, the mains inlet connector was not rated for such low temperatures and might have become very brittle, so it would not be possible to pass safety testing if it had been rated so low. The ethernet magnetics are only rated down to 0 deg C, even though they appear to work fine at -30 deg C. John

A LCD display may not be rated down to -20C so on the meters the OP has the LCD panel may only be marginally working. I wonder what the display would be showing if the zebra type connection (elastomeric connector) between the PCB and LCD was missing a few connections when cold. The electronics may be commanding LL.LL or even -20 but this may not be communicated to the LCD panel

Would it be possible to characterize the device behavior, via watching it with a Kill-a-Watt Meter and a webcam with microphone ? The sound track records noises like the relay used during defrost or the compressor starts. The Kill-a-Watt can show power, like say 500 watts when compressor is running.

If you're not in and out of the refrigerator all that much during certain hours, the compressor cycles should be of relatively equal duration.

If the thermostat is jamming in the "compressor on" state, this may be causing extra-long runs on the compressor. And you could spot the pattern via shooting video of the power numbers. (This assumes you don't already own a power meter with logger output.)

My good multimeter has RS232 output and an optoisolator, so you can record readings once per second or so to a computer. And just measuring the AC current, would be good enough for some of the states a fridge gets into.

A thermostat failure is what killed my previous refrigerator. Close to forty years old, it didn't like running the compressor

Paul

I think the LCD is displaying what the device wants it to display, no dodgy combinations of segments.