It May Be a Dirty Air Filter…
Your evaporator coil is the component in your AC where the refrigerant is evaporated, during which heat is absorbed by that refrigerant before being moved outdoors. If the airflow going over the evaporator coil is impeded by a very dirty air filter, though, that coil is going to get far colder than it should. The condensation that your system removes from the air as it draws heat out of it can then freeze on the coil. This becomes a vicious cycle, as that ice will then further insulate the coil, impeding the absorption of heat even further. Fortunately, replacing your air filter in this scenario is probably all that is necessary to resolve the problem.
…or You May Have a Refrigerant Leak
The dirty air filter is a bit of a best case scenario when there is ice on your air conditioning system, as this could also be the result of a refrigerant leak. When refrigerant leaks out of your air conditioning system, the heat absorption process in the evaporator coil is compromised. Again, the coil will get too cold, and condensation can freeze on it. If you see ice on the refrigerant lines themselves, this is unfortunately very likely the case.
Schedule your AC repairs with the technicians here at Goettl Air Conditioning.