Abstract: In a refrigeration system for a substantially enclosed space and including a compressor, a condenser, an evaporator, conduit means connecting the said compressor, condenser and evaporator to form a cooling circuit, a hot gas by-pass conduit between the compressor and the evaporator, and means provided in the system for apportioning flow of gas between the cooling circuit and the by-pass conduit so that, during a temperature controlling phase of refrigeration, the gas flows both to the condenser and to the by-pass conduit and the apportioning of flow can cause either net heating or net cooling of the enclosed space, the improvement which comprises said apportioning means being in the form of a continuously modulating valve located at the junction of the hot gas by-pass conduit with the cooling circuit between the compressor and the condenser, said valve having a hot gas intake port for receiving hot gas from the compressor, a first outlet port connected to the hot gas by-pass conduit, a second outlet port conn