I have a Intertherm air conditioning unit model#C3QA-047U-B when I want it to cool the coils and piping freeze up and it begins to make a humming noise.

Turn it off
Before you cause damage
Does it have a clean filter?
Has it been serviced,are the coils clean,both outside and inside evaporater coil
Is the blower fan running at a consistent and proper speed?
Does it have a history of being low on refrigerant?
If so it has a leak that need to be fixed,
Refrigerant doesn`t wear out,should need to be added unless it leaks out