I have an '05 Durango that has a similar problem. After operating the A/C for a while at low fan speeds the air flow drops to almost nothing. From what I recall, the TSB issued for mine involves having to install a resistor and/or diode on the temperature sensor at the coils to keep them from freezing up. I've adopted the poor man solution...which is to either run the fan at higher speeds so that it doesn't freeze, or if I notice the drop in airflow because of freezing, turn the A/C compressor off and it returns to 'normal' pretty quickly.