A air conditioning control device is configured to estimate whether or not the temperature of refrigerant on a high-pressure side in a heat pump device is equal to or lower than a predetermined low temperature and to switch a flow path switching device to an air-heating start-up mode when it is estimated that the temperature of refrigerant on the high-pressure side in the heat pump device is equal to or lower than the predetermined low temperature and switch the flow path switching device to a normal air-heating mode when it is estimated that the temperature of refrigerant on the high-pressure side in the heat pump device is higher than the predetermined low temperature.

An air conditioner has a refrigerant circuit and a blower. A refrigerant flow path switching mechanism is configured to switch to a first switching state to allow refrigerant to flow through a reheater, a second expansion valve, and a cooler in this order in a refrigerant circuit. The refrigerant flow path switching mechanism is configured to switch to a second switching state to allow refrigerant to flow through the reheater, the second expansion valve, and the cooler in this order in the refrigerant circuit. The reheater and the cooler are configured to allow air blown by the blower to pass through the cooler and then pass through the reheater during either of the first switching state and the second switching state.

In one instance, a heating, ventilating, and air conditioning (HVAC) system includes a four-way reheat valve and is configured to accesses pressures within a conduit network to facilitate control of the reheat valve. The four-way reheat valve includes a piston valve slide within a main valve chamber and a pilot valve fluidly coupled to the main valve chamber and a compressor-suction conduit fluidly coupled to the four-way valve and to a compressor. The system also includes a flow-restricting device disposed on the conduit downstream of the four-way valve and a pilot conduit coupled to the conduit downstream of the flow-restricting device and coupled to the pilot valve for assisting with movement of the piston valve slide.