Air conditioner and air conditioning system

An air conditioning system comprising:

• an air conditioner that includes:
• an outdoor unit that includes a compressor, an outdoor heat exchanger, and an expansion valve;
• an indoor unit that includes an indoor heat exchanger;
• a refrigerant circuit in which the outdoor unit and the indoor unit are connected to each other by a refrigerant pipe, and performs at least a heating operation in which the indoor heat exchanger functions as a condenser for a refrigerant that is compressed by the compressor and the outdoor heat exchanger functions as an evaporator for a refrigerant that is condensed by the indoor heat exchanger;
• and
• a server that is connected to air conditioner by communication, wherein
• the server includes:
• a first memory;
• and
• a first processing circuitry coupled to the first memory and configured to:
• estimate an amount of refrigerant that remains in the refrigerant circuit by using an operating state quantity of the air conditioner in at least the heating operation,
• the estimating includes a plurality of different estimation models that correspond to ranges of the amount of refrigerant that remains in the refrigerant circuit, and
• one of the estimation models uses, as the operating state quantity, a degree of supercooling of refrigerant at an outlet of the indoor heat exchanger.