We have about a 9 year old TRANE unit in a 2300 sq ft home.

It began freezing up last year.

We have had the coils cleaned, freon levels checked, line blown out, and tried different air filters. The serviceman we use has shaken his head and cannot figure out what is going on. He does say that it seems like it is not getting enough airflow. As soon as we put a filter in there... cheap or expensive, the water starts dripping and we are in for an ice up.

Any ideas?

We now live with a bucket under the air handler.

A few things can make a system freez up. Lack of air flow, Low on refrigerant or metering device at evaporator coil going bad or restricted. We need to start with the air flow. You talk about 1 filter for 2300sq ft. What size is the filter grill and the size of the system will help(make and model).