Abstract: A refrigeration system in which compressors are mounted in one compartment of the housing and condensers and receivers are mounted in an adjacent compartment. Ambient cooling air flows first into the compressor compartment, then into the condenser compartment, and then to the atmosphere. Parallel flow paths from the compressor compartment to the condenser compartment are provided--one flowing the air over the condensers, the other bypassing the condensers, before being expelled. The bypass has a movable flapper valve controlled by the ambient air temperature which causes the ambient air to bypass when its temperature drops below a given point. A shroud encloses the receivers and has a fan-driven heater controlled by the same thermal sensor that controls the flapper valve.