Abstract: Compressor discharge temperature, ambient outdoor air temperature and thermal load are used as control parameters for controlling the expansion valve setting and indoor fan speed. Diagnostics monitor a feedback signal from the fan motor to detect fan over-speed and increased speed due to decreased air flow caused by a dirty indoor air filter. Discharge pressure of the compressor is monitored to detect a blocked outdoor fan. The difference between actual and optimum compressor discharge temperatures and suction pressure of the compressor are monitored to detect a stuck-closed expansion valve or low refrigerant charge. Compressor "short-cycling" is limited to prevent reduced reliability of the compressor. The difference between compressor discharge temperature and outdoor coil temperature is measured before and after startup to detect compressor failure.

Abstract: Compressor discharge temperature, ambient outdoor air temperature and thermal load are used as control parameters for controlling the expansion valve setting and the indoor fan speed. In a variable capacity system the thermal load parameter also controls the compressor capacity. Thermal load is measured by an integrating procedure that increments or decrements an accumulated demand counter value used as an indication of thermal load on the system. The counter value is incremented and decremented based on the room temperature and thermostat setpoint. These same parameters are also used in the overcharge/undercharge diagnostic system.

Abstract: Compressor discharge temperature, ambient outdoor air temperature and thermal load are used as control parameters for controlling the expansion valve setting and indoor fan speed. Diagnostics monitor a feedback signal from the fan motor to detect fan over-speed and increased speed due to decreased air flow caused by a dirty indoor air filter. Discharge pressure of the compressor is monitored to detect a blocked outdoor fan. The difference between actual and optimum compressor discharge temperatures and suction pressure of the compressor are monitored to detect a stuck-closed expansion valve or low refrigerant charge. Compressor "short-cycling" is limited to prevent reduced reliability of the compressor. The difference between compressor discharge temperature and outdoor coil temperature is measured before and after startup to detect compressor failure.

Abstract: Liquid refrigerant temperature, measured by a sensor adjacent the flow control device, provides multiple diverse pieces of information which are used to control the indoor fan speed. liquid refrigerant temperature is used as an indication of outdoor air temperature and is also used as an indication of whether the compressor is operational or not.