The evaporator coil is the cooling element in an air conditioning system. This component uses copper tubing to convey the cold vaporized refrigerant that extracts heat energy from warm return air. When all the parts of the air conditioner are in good working order, you should receive nice cool air at the vents. If warm air is blowing from the vents, you may find that the evaporator coil is frozen. Here’s what to do.