An air conditioning system for a vehicle includes a grille shutter on a front part of a vehicle and arranged in a front face of an engine compartment where a driving source is installed, the grille shutter being capable of adjusting a volume of outside air to be introduced into the engine compartment. A heat source is in the engine compartment. Circulation piping includes a temperature increase section which goes through the heat source. The circulation piping diverges into a vehicle cabin front section and a vehicle cabin rear section from the temperature increase section. A rear air-conditioning controller can limit the volume of air to a rear side of a vehicle cabin when a first condition is satisfied. The first condition is a condition where a grille shutter is stuck in an open state and a defroster function of the vehicle is in an ON state.