I'm considering building some sort of protective structure over our central AC condenser, which sits below a roof pitch where ice dams form and eventually fall right on the unit. Basically, I'm envisioning a non-fancy, moveable dog-house-like structure I can situate over the condenser through the winter, to protect it from falling ice.
If you wrap the condenser (with fabric or plastic, or put walls around it), it won't be air-tight but it will trap moisture inside, you'll get rust.
Instead, put a piece of plywood on top and weigh it down with a rock (or a brick if you want the spendy solution). Protects from falling ice or snow build-up inside the unit, and allows the unit to dry out normally after each storm.