The invention relates to an air conditioner for a motor vehicle, comprising a coolant circuit (1) that is provided with several heat-transferring devices through which a coolant can be directed, a heat-transferring device (12) also being part of a coolant circuit. Coolant is redirected from portions of the coolant circuit (1), which are shut down during heating, into a portion of the coolant circuit (1), which is active during heating, as required. Also disclosed is a method for operating such an air conditioner.