Air conditioning system

An air conditioning system comprising:

• a heat pump unit including a radiator usable with a refrigerant;
• a gas furnace unit including a heating section configured and arranged to heat passing air;
• a blower configured and arranged to generate an air flow that passes through the radiator and the heating section;
• a first temperature sensor provided in a room, the temperature sensor being configured and arranged to detect an indoor temperature in the room;
• and
• a controller configured and arranged to control each action of the heat pump unit, the gas furnace unit, and the blower,
• the controller being configured to cause the gas furnace unit to operate as a heat source unit when the indoor temperature is less than a set temperature set by a user and a difference value obtained by subtracting the indoor temperature from the set temperature is equal to or greater than a first threshold at startup,
• the controller being further configured to cause the heat pump unit to operate as the heat source unit when the difference value is less than the first threshold at startup,
• the controller being further configured to prohibit both of switching from the heat pump unit to the gas furnace unit and switching from the gas furnace unit to the heat pump unit until a predetermined time has elapsed, in which the controller starts counting of the predetermined time each time a switching of the heat source unit is executed, and
• the first threshold being set as a value whereby the indoor temperature reaches the set temperature in less time by causing the gas furnace unit to operate as the heat source unit than by causing the heat pump unit to operate as the heat source unit when the difference value is equal to or greater than the first threshold.