Fridge/Freezer Issue

DJBenson

About six months ago I woke up to find out fridge/freezer (a CDA American-style unit) unresponsive aside from the temperature display which was a couple of degrees below freezing on the freezer side. We reported it to CDA who attended and as the unit had come back on could not diagnose an issue.

After that happened, I purchased a digital thermometer to keep an eye on the temperatures and thought nothing more of it until I recently connected those sensors to my home automation system (yes I know ) and set some alerts. I have since seen the freezer regularly go above -18 (-9 is the highest I've seen) and the fridge to +5 when they are set to -8 and 4 respectively.

This is happening throughout the day/night so cannot be attributed to the unit being opened/filled/switched off/any other excuse the manufacturer can think of.

What I'm not sure of (because who monitors their freezer right?!) is are those kinds of spikes "normal"? They last for a short period of time but to me it does not sound safe for the internal temperature to exceed -18 degrees.

The two graphs show my fridge and freezer temperatures over the last 24 hours and the bottom two show a comparison of the digital readout and a mechanical readout from the exact same spot in the freezer (and the photo was taken only when the alert that the temperature had increased happened so again the temperature cannot be attributed to external factors).

Any thoughts (aside from "you sad <insert choice of expletive here>")?

neilmcl

The fridge temp looks pretty normal to me if set at +4C. The FF will constantly adjust the temp as it goes through it's normal auto defrost cycle, I assume it's frost free. Do you keep the freezer full?

What exactly have you hooked up to your "home automation system"?

DJBenson

The freezer is normally about 2/3 full between fills and is indeed a frost free model. I’ve just looked back over the past week and it’s been as high as -8 in the middle of the night. Normally lasts about half an hour before the temperature starts to return to safe levels.

The sensor is a 433mhz fridge/freezer thermometer which connects to the LCD display shown above. It just so happens you can pick up that signal with a 433mhz receiver (an rtl_sdr if you’re interested). Domoticz receives a reading for the fridge and the freezer every minute.

I purchased the mechanical thermometer to validate the readings of the digital device as they were so wild I didn’t believe them at first but it’s accurate within a degree or so of the Salter unit so I’m confident the values are correct.

I’m concerned why the freezer itself decides not to report these spikes, it could be the location of the sensor for the door remains colder than the two I use but still, -23 to -8 is a huge swing (the worst I recorded and is not shown in the above graphs).

EssexExile

The big rises in temperature in the freezer are defrost cycles when the heaters come on to melt the ice, I assume it wouldn't report anything during that time.

The rest is what I'd expect from CDA, just about good enough.

DJBenson

EssexExile wrote: »

The big rises in temperature in the freezer are defrost cycles when the heaters come on to melt the ice, I assume it wouldn't report anything during that time.

The rest is what I'd expect from CDA, just about good enough.

Interesting, thanks. I hadn't considered looking into what "frost free" means on.a technical level and I hadn't considered for one moment that it meant heating up the freezer from the inside :rotfl:

I guess that's why the temperature changes are so extreme and so rapid - a freezer without power would not gain temperature as quickly as this is showing so it makes sense that it's the expected behaviour.

neilmcl

DJBenson wrote: »

Interesting, thanks. I hadn't considered looking into what "frost free" means on.a technical level and I hadn't considered for one moment that it meant heating up the freezer from the inside :rotfl:

I guess that's why the temperature changes are so extreme and so rapid - a freezer without power would not gain temperature as quickly as this is showing so it makes sense that it's the expected behaviour.

At the end of the day the spikes in temperature will make little to no difference to the food stored in the freezer as long as the overall average temp is between -18C and -20C then that's all OK.