Following are some preventive measures for the freezing of the evaporator:
1. Check the air flowing through the supply registers. Air should not be warmed or trapped inside.
2. There should not be a moisture built up inside.
3. Condensate lines are the part of your HVAC system that drains away excess moisture from humidity. This moisture, condensed into water, travels through pipes to a floor drain. If the water is stuck in one place because of a clogged pipe, it can freeze. so, the water should not be stuck in one place.
4. Shut the unit off if evaporator has got frozen and try to melt the ice.