The invention relates to a method for operating an air conditioner (1) for treating the air of a passenger compartment of a motor vehicle. The air conditioner (1) exhibits a refrigerant circuit (2) configured for a combined cooling unit and heat-pump mode and for a post-heating mode. In the heat-pump mode with a first and a second heat source, two heat sources differing from each other can be used. A temperature of the first heat source, a temperature of the second heat source, and a regulation characteristic number and a maximum pressure are taken into account in the refrigerant circuit (2) for operating the air conditioner (1) in a heat-pump mode. The invention additionally relates to a method for switching between the two heat-pump modes.