In a calculation process, a control unit calculates a feature quantity from a physical quantity obtained from a device within a predetermined period. In an estimation process, the control unit estimates the state of the device, based on the feature quantity calculated by the calculation process. In a restriction process, the control unit restricts the estimation process when an estimation restriction condition is satisfied, maintains restriction of the estimation process until a standby release condition is satisfied when a restriction release condition is satisfied, and releases the restriction of the estimation process after the standby release condition is satisfied. The estimation restriction condition is a condition in which there is a possibility of occurrence of erroneous estimation in the estimation process. The restriction release condition is a condition in which the erroneous estimation in the estimation process is suppressed.

A method can include fluidically coupling a pump between at least two heat exchangers, confirming that an expansion valve is at least partially open, starting a compressor, beginning a first preselected time period, starting the pump, stopping the compressor once the first preselected time period ends, at least partially closing the expansion valve, beginning a second preselected time period, monitoring a differential pressure across a first point downstream of the pump and a second point upstream of the pump, indicating improper pump installation if the differential pressure does not exceed a first threshold before the second preselected time period has ended, stopping the pump, or any combination thereof. The expansion valve can be fluidically coupled between the pump and one of the heat exchangers. The compressor can be fluidically coupled between the two heat exchangers.