Abstract: In a system having a waste heat recovery subsystem utilizing a heat exchanger, such as a refrigeration system having a heat exchanger for extracting and recovering heat energy from the superheated refrigerant by means of a transfer fluid, method and apparatus for control of the heat recovery subsystem. A combination of three interactive control systems is provided for control of the flow of the heat transfer fluid through the heat exchanger. A first heat sensor means determines when the waste heat temperature is sufficiently high, controlling a pump to obtain circulation of the fluid when such temperature exceeds a preselected value. A second heat sensor means monitors the temperature of the heat transfer fluid and stops circulation of the fluid when such temperature exceeds a preselected safe upper limit.