Method for regulating a condenser in a thermal cycle apparatus, in particular in an ORC apparatus, wherein the thermal cycle apparatus comprises a feed pump for conveying liquid working medium with an increase in pressure to an evaporator, the evaporator for evaporating and optionally additionally superheating the working medium with a supply of heat, an expansion machine for generating mechanical energy by expansion of the evaporated working medium, a generator for at least partially converting the mechanical energy into electrical energy, and the condenser for condensing the expanded working medium, and wherein the method comprises the following steps: determining, in particular measuring, a rotational speed of the generator or of the expansion machine; determining, without the use of a temperature sensor, a temperature of cooling air supplied from the condenser; determining from the determined generator or expansion machine rotational speed and the determined cooling air temperature, a condensation setpoint pressure at which the net electrical power of the thermal cycle apparatus is at a maximum; and controlling or regulating the condensation pressure, with the condensation setpoint pressure as target value, in particular by adjusting a condenser fan rotational speed; characterized in that the determining of the cooling air temperature without using temperature sensors comprises a calculation of the temperature from a determined rotational speed of the generator or the expansion machine, a determined rotational speed of the condenser fan and a determined condensation pressure; or wherein determining the cooling air temperature without using temperature sensors comprises sampling the temperature from a predetermined table depending on a determined rotational speed of the generator or the expansion machine, a determined rotational speed of the condenser fan, and a determined condensation pressure. determining, in particular measuring, a rotational speed of the generator or of the expansion machine; determining, without the use of a temperature sensor, a temperature of cooling air supplied from the condenser; determining from the determined generator or expansion machine rotational speed and the determined cooling air temperature, a condensation setpoint pressure at which the net electrical power of the thermal cycle apparatus is at a maximum; and controlling or regulating the condensation pressure, with the condensation setpoint pressure as target value, in particular by adjusting a condenser fan rotational speed; characterized in that the determining of the cooling air temperature without using temperature sensors comprises a calculation of the temperature from a determined rotational speed of the generator or the expansion machine, a determined rotational speed of the condenser fan and a determined condensation pressure; or wherein determining the cooling air temperature without using temperature sensors comprises sampling the temperature from a predetermined table depending on a determined rotational speed of the generator or the expansion machine, a determined rotational speed of the condenser fan, and a determined condensation pressure.