I have yet to come across a so-called "Auto-Defrost" refrigerator/freezer that works efficiently.
Most use a small fan to circulate the cooling air, a drop of moisture on the blades is enough to freeze & stop the fan.
When the unit goes into defrost mode the fan stops and theoretically ALL the ice is removed from the Evaporator plates.
(The condenser is the cooling coil mounted externally to cool the compressed gas & liquify it..."condense")
(Not always visible these days.)
The defrost mode ends at a preset temp & cooling starts again..but with the fan in a "paused state"....this is the period when any moisture droplet on a fan blade gets frozen.....thus preventing rapid cooling down of the storage area on restart. (The motor is a synchronous type..... uses very little current, generates very little heat....but is very weak!)
In my personal view, it is better to remove covers, remove ice, wipe down any moisture remaining on the evaporator and surrounding areas...including the fan blades...... I know it negates the whole point of having auto-defrost, but I think you will find your fridge/freezer operates much more efficiently if done at intervals. And it needn't take long...20 minutes tops. All models are different of course & indeed, not all use a fan motor. But the principles are the same ....air ducts get blocked with ice and the auto defrost fails to remove it all.... when the fridge restarts, the remaining ice quickly attracts the moisture in the air (Nice, moist warm air...entering when you open the door!) and reforms..... and the vicious cycle is repeated.
Hope that helps. Kind regards.