Evaporator coils contain the system's refrigerant as it converts from liquid to gas. The refrigerant moves through an expansion valve and into the evaporator coils. The liquid refrigerant moves through an expansion valve decreases pressure on the liquid refrigerant thus reducing by absorbing heat from the evaporator coil transfer occurs in these coils, creating a cold surface. The blower moves air across the cold surface, creating the conditioned air that cools your home. The gaseous refrigerant moves to the outdoor unit Condenser coils in the outdoor unit house the refrigerant during its return to liquid form The compressor increases pressure on the gas, using it to condense into liquid. As the refrigerant changes state, it release the heat it contains. The heat is dispersed into the air outside. The liquid refrigerant moves back inside for the cycle to begin again. There is really no difference between a Hot water coil and a Chilled water coil in construction. Hot water coils are usually 1 or 2 rows and chilled water coils are usually 3 to 12 rows deep. The vast majority of chilled water coils are constructed from either 1/2" OD tubes or 5/8" OD tubes