Are existing next sensors in HA:
- energy meter for refrigerator,
- room temperature,
- room humidity.
How to create automation, which will be informed, when is time to defrost the refrigerator?
Thank you.
Are you sure home automation is the answer here?
The vast majority of modern refrigerators and freezers automatically perform defrost cycles daily. If you are having frosting issues you probably need to do some fridge maintenance or repair.
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Yes, in automation (like bathroom extracting fan).
My mistake, when I writing refrigerator, mostly I mean combined refrigerator and freezer, and defrost is mean for freezer part (because you can´t skip the physis).
Your refrigerator's freezer does not have a self-defrost feature?
What is its brand, model, and age?
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True, but as mentioned above, development" also occur on these kind of utilities.
Previous it was recommended once/twice a year , New merchandises don't need it ( manually ) so often , depending upon how often you open the Freezer, or whether you keep the door open to long, or impatiently stuff in preperred food which is not cooled down enough etc.
So When/if you see i.e half an inns ice on the shelf's IT's about time, put a sticker on the Freezer, so you don't forget , Cause im sure you don't plan this, and you might notice it when he Freezer is Full 
... and as also mentioned above, their could be a "routine behavior" which should be change also, if you find you need to defrost a New Freezer manually once a year
Are you asking about how to integrate defrosting into your cooling appliances, or how to set a date for defrosting into a calendar?
No im not, so don't reply to me
Thank you @boheme61, @IOT7712
I am searching how to integrate sensors to make a notify "now is the time to manual defrost". When you not used freezer too much, but in family are more childrens, often opens and closes the door (especially during hot days) or openned too long, etc.
As i said, a manual inspection is the most reliable way, however you can place i.e an Aqara-zigbee sensor( Temp / Humid ), to alarm for i.e low temp, high humid. and use the "history-graph" to trace i.e bad behaviors/time.
Together with a Door-Sensor which clock time Opened and how often
And in regards to the Children's "behavior" sometime the hard way, is the most effective , Don't fill it with ice-cream if they don't listen to your " Advises" , use economic causes, a new fridge/freezer cost, daily (electricity) and when it need to be replaced/repaired do to "misuse" == No Ice Today 
It's Not that the Cold gets out that create ice-buildup. But the warm-air's Humid gets in, " in an instant " and gets in contact with the + ( -18 -24 ) inside , that "Kills It" ... in the long run
From the Wikipedia link I posted earlier, here is how the self-defrost feature works.
The defrost mechanism in a refrigerator heats the cooling element (evaporator coil) for a short period of time and melts the frost that has formed on it.[1] The resulting water drains through a duct at the back of the unit. Defrosting is controlled by an electric or electronic timer. For every 6, 8, 10, 12 or 24 hours of compressor operation, it turns on a defrost heater for 15 minutes to half an hour.
In summary, it periodically heats the cooling element to melt any frost that may have accumulated on it. The interval is based on how long the compressor operated (i.e. how many hours). It's not based on the temperature or humidity inside/outside of the refrigerator.
It's still surprising that you need to manually defrost the refrigerator's freezer compartment.
Refrigerators have had self-defrost for decades so if yours needs to be manually defrosted then it means its self-defrost has failed.
Repairing it leads to a better and more convenient outcome (automatic defrosting) compared to using sensors and calculations to predict when you must manually defrost it.
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First you need to know what condition CAUSED the defrost need. Do you have a detailed set of conditions that tells you when?
(read: begin with the end in mind. What is the goal. How do I know. Ok what sensors can give that info...)
If you don't know how to tell when it's time from your device in a way you can sense... don't even bother trying the automation.
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No all. I bought a dorm-size refrigerator when my daughter went to college and it does not have automatic defrost.
There is a simple way to integrate into Home Assistant. Monitor the power usage. It is normal for a refrigerator without automatic defrost to run continuously when the evaporator coils are covered with ice because the fan can't force air through ice, and the thermostat will never see cold air.
So all you need is a power-sensor (NOT A SWITCH). If the refrigerator runs for an hour non-stop, then a defrost is likely needed.
NOT A SWITCH. The relays in switches are rated for resistive loads only, and a refrigerator is anything but resistive. Shelly does make a power monitor module that should work for this purpose.
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It's the size of a dormitory?
/s
FWIW, the OP has overlooked to provide the make and model of their appliance other than it's a refrigerator with a freezer compartment ... and most kitchen refrigerator/freezers are equipped with self-defrost.
The fact this one apparently doesn't leads to the question: Does it genuinely lack the feature or is just broken?
- Self-defrost is broken: fix it.
- No self-defrost: Create a periodic reminder to manually check if it needs defrosting
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@steveman thanks for Shelly.
Otherwise the fridge has defrost, the freezer doesn't (I should have written the first question more precisely - my experience). To be honest, I was expecting technical ideas, but I didn't know there were so many great fridge repairmen here.
At the risk of sounding like a contrarian, the energy-monitoring smart plugs I use are rated "general-purpose up to 8A" (higher if the load is purely resistive).
FWIW, I bought a dozen of them years ago ($5 each) and replaced their firmware with Tasmota.
I have been using several to monitor the power consumption of motorized devices including a refrigerator, dishwasher, gas furnace, washing machine, and a range hood. They're all motorized devices with the washer and furnace (blower) representing the highest current draw.
They're all configured to automatically turn on after a power failure and have been working well for several years.
Again, what is the make and model of this appliance?
Because it's normally the freezer compartment that develops frost because its temperature is below freezing, so it has a self-defrost function.
Cold air is created in the freezer compartment and is blown into the refrigerated compartment through a thermostatically controlled vent.
The refrigerated compartment's temperature is normally slightly above freezing so it doesn't develop frost.
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