There are many reasons why you could see your air conditioner or specifically the evaporator coils solidify into ice.
However, it is always due to the fact that the fluids are unsuccessful in adaptation to the heat in the area in colder temperatures and vice versa in elimination of heat with warmer temperatures.
In other words, saturation requirements are not met before the refrigerant fluid was able to arrive at the compressor thereby compelling a reaction that generates a condensation process that ices up instead of regularly flowing as it is supposed to due to the lower than normal temperature.
Once this is noticed, the initial step to always take is turning the air conditioner off and letting it defrost.
Switch it to heating mode for faster thawing.
Seeing that these are the main actions that explain such a freezing phenomenon with evaporator coils, there are some concrete influences that will certainly lead to such results.
The first main and most common reason is related to the condition of the coil.
Whether it has a very dirty filter or has a clogged duct, your air conditioner will most likely freeze if the current flow is interrupted.
In this case, the solution is very simple.
You just have to determine what the reason for the obstruction is and remove it.
Take the air conditioner apart or have it done by a professional and clean everything to ensure that it will not happen anytime soon as this is quite normal for most HVAC.
Another factor that you should look into is having too little quantities of fluids or refrigerants which is most likely by leakage.
In this case, one sign you can rely on is if the coil has frozen up and if the temperature you have set it in is not correct.
On that note, your suction pressure is off and should be fixed by an expert HVAC technician after melting the ice.
What the technician will basically do is detect the coil leaks and either solders and seals it or replaces the whole system if there is too much damage that ordinary repairs will simply not do.
If this is still not the case, try to look at the condition of the coil fins.
For apparent reasons, your air conditioner will not only freeze but also function improperly if the coil fins are impaired either by being twisted or compressed.
The reason behind this is somewhat related to the first cause as it will result in an obstruction to the refrigerant flow and air current.
Again, this is a job for an HVAC technician but if you want to handle it on your own, you must first be able to assess how badly damaged the fins are.
If they are fixable with a few poundings here and there, go ahead but the conditions of fins are usually too severe that blockage results.
You can either replace the coil fins or the whole system depending on the extensity of the damage.
The blower or the fan for the cooling coil may also halt function causing it to ice up.
Such a factor can be due to the capacity of the motor that powers the fan, the blower diminishing in power or perhaps the blades of the fan being too restricted or too detached leading to a fan belt that is impaired as well.
If it is a motor problem, try and see if cleaning it will be able to fix the problem.
If not, take it to a mechanic to fix the inside.
For reasons of the blade, adjust it manually to the proper fitting.