Abstract: A reverse cycle refrigeration apparatus for air dehumidification is employed having an evaporator and a condenser and employing first and a second heat transfer coils for this purpose. Both coils are positioned in the air stream. In a first cycle the second coil functions as the evaporator for cooling and dehumidifying the air stream and accumulating frost and the first coil acts as the condenser, warming the cooled and dehumidified air stream and thawing frost having accumulated on it. In a second cycle the first coil acts as the evaporator, cooling and dehumidifying the air and providing the heat for defrost and the second coil acts as the condenser, thereby being defrosted. Dampers are provided for stopping air flow over the defrosting coil.