One of the most frustrating problems with a window air conditioner is if it starts to ice up. For the owner of the air conditioner is can be perplexing.
When this problem occurs most people immediately think it is the fault of the refrigerant gas. More often the cause is the result of other difficulties.
It is most often the result of poor airflow.
Any time the airflow through an air conditioner is restricted the cooling system becomes affected. If taken to extremes the critical pressure-temperature balance of the cooling coil can be changed. If they drop too low the cooling coils surface temperature can drop below the dew point temperature of the room. When this happens the cooling coil will begin to operate as a refrigerator rather than an air conditioner. Rather than simply cooling the air it will collect and hold moisture. The moisture will freeze onto the cooling coil where it will appear as ice.
A larger air conditioner will not always provide more cooling. It should be sized for the room area. If properly sized it should operate long enough to remove moisture from the air. It is the moisture removed from the room which actually produces the feeling of cooling. Unfortunately many people in their rush to purchase a window air conditioner buy too large a model.
An air conditioners primary job is to remove moisture from the room to give us a feeling of comfort. During this process they create a lot of water. How much, is dependent upon humidity in the air, 
