Basic idea with frost free is the cooling parts are kept behind a partition so the cool air only gets into freezer when the fan runs, so on the defrost cycle the heat from defrost heater does not reach the food as fan is not running.
There are a number of things which can go wrong, clearly if the heater fails then it will not defrost, or the timer which turns on the heater fails, again it will not defrost.
However if the drain hole blocks also it can't defrost, so simply some thing not allowing the door to close fully and as a result for there to be more than normal amount of ice can mean it does not fully defrost in the cycle so the ice builds up.
Also damaged insulation can cause more ice in some areas which in turn causes the problem.
The engineers who work regular on the freezers recognise the faults. Often they know were ice builds up, or have a computer which can down load a record of what has gone on. However for likes of you and me, not so easy.
My freezer has an inverter drive (Samsung) so putting an energy meter on the freezer running it takes around 60W and defrost around 120W so if I see 120W as the maximum power I know it has done the defrost cycle. However cheap freezers don't use inverters so the start up current is over 120W so with cheap meter one would need to manually watch the meter.
More expensive energy meters can show a graph on the PC. With my Energenie MiHome meter I can see how often and for how long the defrost heater has been running for, however other information is not shown so it does depend what you want from the meter the cheap one is better for some things.
I use the cheap meter with the new freezer and fridge/freezer to show how much power it uses per year, normally a little more than the label says, but not too much over, if the door is closing as it should, and the insulation is good, then average power will be as the energy
https://www.diynot.com/diy/label says. However if the insulation is damaged then the power used will be way over what the label states.
I have one old fridge/freezer which is damaged and is now used to brew beer in only. On switch on when first used all seems A1, but as it runs ice builds up in the insulation, so after 3 weeks running it is using way over the power it should, to a point where it hardly ever turns off. Since beer brewing does not get it cold enough for ice to build up, it does that job great.
So yours should use 243 kWh/annum so 666 watt hours/day so I would say if energy meter shows 700 watt hours / day or less then likely OK, if over that then insulation likely damaged. I would expect the motor to use around 60 watt running, and the heater will likely use 100 watt.
