There are only two potential causes for that, restricted refrigerant flow at the metering device at the coil, or low on refrigerant, most likely the latter.
In either case it is going to take a technician with a set of service gauges to determine which is the case and either fix the leak and restore the refrigerant charge, or clean the line strainer ahead of the metering device, or get rid of the tiny ice ball *inside the metering device that is restricting flow.
These things unfortunately are often misdiagnosed. You can eliminate a diagnoses of moisture inside the sealed system by turning the unit off, until all the ice melts for a few hours, then turning it back on, if the largest copper tube coming from the cooling coil then runs cold enough to sweat for a few minutes then it was water inside the sealed system.... if no... then you most likely have a refrigerant leak that needs to be located and repaired and refrigerant added ($350 to $650 usually).
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