I worked with auto defrost 1980 so not really that new, as to the every so often needing a defrost not sure if all freezers are like that or just faulty ones. I have a Hotpoint fridge/freezer plumbed in with cold water from the door, it must be now around 20 years old, maybe older, from the day we got it I think it was faulty, however simply did not realise, it was on a maintenance contract so if it went wrong we called some one out.
It would go wrong about every 2.5 years, first thing we would do is a defrost, if that failed then call the guy out, so first time he renewed a board, next time he removed the cover at back showing us the huge build up of ice, which had stopped the fan running, he blamed this on the drain freezing up and becoming blocked, he put some copper wire in the hole to transfer the heat from defrost heater to whole, and it seemed to work, having seen the build up of ice, next time it went wrong I defrosted for a lot longer, with a fan running inside the freezer compartment to assist rapid defrost, this seemed to work as said not that often it needed doing.
The years went by and then we got a fault with the inertia lamp flashing on/off and the motor switching on/off with very little time between, called the guy out, this time not defrosted first as did not seem connected. He opened the fridge door (not freezer) saw a lump of ice at back, and simply said uneconomical to repair, seems the insulation was faulty, because I had been defrosting it first on previous call outs, they had not seen the tell tail signs. It seems water from within the room builds up in the insulation and allows the heat into the unit through the water, a full defrost and all the water runs out of the insulation and it works again, until the frozen water builds up again.
So insurance paid out and we got a new fridge/freezer with 10 year warrantee, however old one not thrown out, it is now doing sterling surface as a brew fridge, since only cooling to 19°C no build up of water and faulty insulation does not really matter, since frost free and no evaporators in the way, bottom draw of freezer left in with bulbs in it as heaters, and fermenter sits in second draw, all others removed. Beer stays in freezer for around 5 to 8 days, then moved to fridge compartment, temperature is raised to 22°C likely another 7 days then bottled.
Two external thermostatic controllers are used to switch on heater or freezer motor as required, the fridge will only start cooling once freezer hits target so in real terms fridge is never cooled.
So 40 pints at 22°C set to 19°C monitoring the actual fermenter not the air for the thermostatic control, the unit will run for around 45 minutes and the air temperature drops to 8°C but the fermenter stays at 19°C after around 1/2 hour it starts to warm up again and motor runs for second time, and after that around once every 5 hours in summer, until day 2 when most of the fermenting is finished, what was a surprise was it did not over shoot. I realised this is due to the fan stopping when thermostat cuts out, so there is very little air movement once it stops, this stopping and starting of the fan will of course also help when being used as a freezer.
Since I have a small freezer which is not frost free I decided to monitor both frost free and non frost free, actually using the thermostats I use for brewing just to measure temperature, and there was a marked difference, non frost free motor started at -15°C and stopped at -19°C it did vary according to where the sensor was placed, and how much food in it, crammed full with sensor at top -17°C to -19°C near empty with sensor in centre around -15°C to -17°C so then the frost free, the first thing was the range was much reduced -17°C to -18°C and second did not seem to matter where the sensor was placed, got the same results.
Since having the inverter drive freezer and fridge/freezer I have not needed to defrost, now around 4 years old, so seem the Hotpoint may have been faulty from new, also because there is no inrush when starting I can see with an energy meter each time the defrost cycle runs, around once a day, it uses 120W defrost and around 60W running, I have only used the stand alone energy meter so can't say exactly when heaters cut in.
I let the unit cool then over 7 days measured the power used, times by 52 and it is a little lower than what it says it should use for the year. If the insulation fails then the power used will sore, so once a year I can test to see if insulation is OK, however working on a 10 year life swapping a fridge or freezer because it's using too much power is not likely to save one any money, swapping because it can't get down to set temperature yes needs changing, but you should realise if the motor never turns off without need for power meter.
I had a freezer do that, but when measuring the temperature it was -25°C so it was thermostat gone, not insulation or loss of gas. Again at that time I did not have a thermometer which would go low enough, however freezing point of saturated brine is -18°C so since the salt water froze it was easy to see the thermostat was faulty.
Oh and yes the chest freezer is by far the cheapest to run.
