An automotive air conditioning system has a primary hot water circuit 11
located on a side where a vehicle installed heat generator 10 is located
and a secondary hot water circuit 13 which includes a hot water type
heater core 12 for heating passenger compartment outlet air, whereby when
in a heating mode, in the event that a coolant temperature TW1 of the
primary hot water circuit is lower than a coolant temperature TW2 of the
secondary hot water circuit 13, an opening and closing valve 26 is
closed, whereas an opening and closing valve 23 is opened, so that a
state is created in which the hot water circuits 11, 13 are separated
from each other. On the other hand, in the event that the coolant
temperature TW1 of the primary hot water circuit becomes higher than the
coolant temperature TW2 of the secondary hot water circuit 13, the
opening and closing valve 26 is opened, whereas the opening and closing
valve 23 is closed, so that a state is created in which the hot water
circuits 11, 13 are connected to each other.