Vehicle air conditioner with hot-gas heater cycle

An air conditioner for a vehicle, comprising:

• a heating heat exchanger which heats air to be blown into a compartment of the vehicle using hot water in a hot water system mounted to the vehicle;
• a refrigerant cycle which is provided with a compressor for compressing refrigerant, an exterior heat exchanger for cooling refrigerant discharged from the compressor, a decompression unit which decompresses refrigerant, an interior heat exchanger for performing heat exchange with air, and an accumulator for separating refrigerant into gas refrigerant and liquid refrigerant and for storing the separated liquid refrigerant therein;
• a bypass passage through which the refrigerant from the compressor is introduced into the interior heat exchanger while bypassing the exterior heat exchanger in a hot-gas heating mode for heating the compartment;
• a switching valve which switches one of the hot-gas heating mode, and a cooling mode for cooling the compartment in which refrigerant flows through the compressor, the exterior heat exchanger, the decompression unit and the interior heat exchanger;
• an electrical heater, attached to an outer side of the accumulator, for heating the accumulator;
• a control unit which controls the switching valve and the electrical heater,
• wherein the control unit includes:
• a switch which indicates that the hot-gas heating mode is requested;
• a first sensor which detects a condition indicating a heating load, including at least one of an air temperature outside the compartment and a water temperature of the hot water system;
• a second sensor, which is attached to the electrical heater, and senses a temperature of the electrical heater and a refrigerant temperature inside the accumulator;
• first means for switching the switching valve to set a mode other than the hot-gas heating mode, turn off the electrical heater and stop the compressor, when the hot-gas heating mode is requested by the switch and when the detected temperature of the first sensor is higher than a first set temperature;
• second means for switching the switching valve to set the hot-gas heating mode, turn off the electrical heater and operate the compressor when the hot-gas heating mode is requested by the switch and when the detected temperature of the first sensor is lower than the first set temperature and is higher than a second set temperature;
• third means for switching the switching valve to set the hot-gas heating mode, turn off the electrical heater and operate the compressor when the hot-gas heating mode is requested by the switch, when the detected temperature of the first sensor is lower than the first set temperature and is lower than the second set temperature, and the detected temperature of the second sensor is higher than a predetermined temperature;
• and
• fourth means for switching the switching valve to set the hot-gas heating mode, turn on the electrical heater and operate the compressor when the hot-gas heating mode is requested by the switch, when the detected temperature of the first sensor is lower than the first set temperature and is lower than the second set temperature, and the detected temperature of the second sensor is lower than the predetermined temperature.