I turned our air conditioner on last night because it was literally 85 degrees in our house. When I turned it on I immediately knew something was wrong. It had that strange whistleing noise. It did this last summer, but when we would change the filters it quit. So I shut it off and this morning changed the filters and turned it back on. Within ten minutes I took the cover off and the coils were starting to freeze again. What gives?

Icing coil is ALMOST ALWAYS low airflow or low on refrigerant.