Vehicular heat management system

A vehicular heat management system comprising:

• a low-pressure side heat exchanger configured to cool a heat medium by heat exchange between a low-pressure side refrigerant of a refrigeration cycle and the heat medium;
• a first heat medium circuit in which the heat medium cooled by the low-pressure side heat exchanger circulates;
• a high-pressure side heat exchanger configured to heat a heat medium by heat exchange between the high-pressure side refrigerant of the refrigeration cycle and the heat medium;
• a second heat medium circuit in which the heat medium heated by the high-pressure side heat exchanger circulates;
• and
• a switching device configured to switch a mode between a communicating mode in which the first heat medium circuit and the second heat medium circuit are coupled and a non-communicating mode in which the first heat medium circuit and the second heat medium circuit are not coupled, wherein
• the switching device selects the communicating mode when a temperature of the heat medium that flows in the first heat medium circuit is lower than a first predetermined temperature, and
• the switching device selects the non-communicating mode when the temperature of the heat medium that flows in the first heat medium circuit is higher than or equal to a second predetermined temperature.