PTC supplementary heater for a motor vehicle

PTC heater, especially for a motor vehicle heating or air-conditioning system, comprises one or more PTC elements that convert electrical power into heat. A control unit evaluates measurement values from a device monitoring electricity consumption and accordingly controls the power supplied to the PTC heater. Independent claims are also included for: (1) Process for operating the above PTC heater; and (2) Heating or air-conditioning system, especially for a motor vehicle, comprising a heat exchanger and the above PTC heater.