a refrigerant system is provided where the functions of an economizer heat exchanger and liquid - suction heat exchanger are combined . the two configurations are disclosed with a single common heat exchanger construction . in a first configuration , a series of valves selectively routes only one of two possible refrigerant flows through a common heat exchanger such that a control can selectively activate either an economizer heat exchanger circuit or a liquid - suction heat exchanger function . in a second configuration , both refrigerant flows are passed to the common heat exchanger through separate fluid lines and are selectively activated by the control . variations of the second configuration are also disclosed .