AbstractSome methods are discussed for detecting the formation of ice on the evaporators of air‐source heat pumps and air coolers by electronic means. the sensing of thermal resistance caused by ice build‐up can be done by measuring temperature differences between the evaporator and the air, and analyses are presented of the effect of using both linear and non‐linear temperature sensors for this purpose. the direct detection of the presence of ice can be done by measuring the capacitance of a suitably‐placed pair of plates, and the performance of such a system is analysed. Preliminary reports are presented of the use of both of these methods of ice detection in the defrosting of an experimental he