Abstract: A system and a method are provided for returning oil in a heating, ventilation, and air conditioning (HVAC) system by determining when an ambient zone temperature is equal to or less than a temperature limit and reversing a direction of refrigerant flow of the HVAC system based on the length of time. Also, a system and a method are provided for monitoring the length of operation in a first and a second heating mode and for reversing a direction of refrigerant flow based on the length of time operation occurs in the first and second heating modes. A system and a method having a first compressor, a first heating mode, a second heating mode, a defrost mode, and a controller is disclosed. The controller selectively controls initiation of the defrost mode in response to an HVAC system operating in a heating mode of operation for a predetermined amount of time.

Abstract: A system and method is provided for monitoring a system pressure to infer whether a high pressure cut out (HPCO) switch has opened disabling a heating, ventilating, and air conditioning (HVAC) compressor. A system and method are also provided for determining whether to disable the HVAC compressor based on a status of a low pressure cut out (LPCO) switch, an ambient temperature, and system mode state. The systems and methods may be used interchangeably with the appropriate adjustments to decision limits, such as where the LPCO may be monitored to infer status and the HPCO status may be directly used with temperature and system mode state.

Abstract: A system and a method are provided for powering up a heating, ventilation, and air conditioning (HVAC) system and operating a sump heater for a compressor for a first predetermined period of time in response to the HVAC system being powered up. A heating, ventilation, and air conditioning system and a method for controlling the system are provided. The HVAC system includes a compressor, a sump heater associated with the compressor, and a controller configured to control the compressor and the sump heater so that the sump heater is not operated while the compressor is operated.

Abstract: A system and a method are provided for returning oil in a heating, ventilation, and air conditioning (HVAC) system by determining when an ambient zone temperature is equal to or less than a temperature limit and reversing a direction of refrigerant flow of the HVAC system based on the length of time. Also, a system and a method are provided for monitoring the length of operation in a first and a second heating mode and for reversing a direction of refrigerant flow based on the length of time operation occurs in the first and second heating modes. A system and a method having a first compressor, a first heating mode, a second heating mode, a defrost mode, and a controller is disclosed. The controller selectively controls initiation of the defrost mode in response to an HVAC system operating in a heating mode of operation for a predetermined amount of time.

Abstract: A system and method is provided for monitoring a system pressure to infer whether a high pressure cut out (HPCO) switch has opened disabling a heating, ventilating, and air conditioning (HVAC) compressor. A system and method are also provided for determining whether to disable the HVAC compressor based on a status of a low pressure cut out (LPCO) switch, an ambient temperature, and system mode state. The systems and methods may be used interchangeably with the appropriate adjustments to decision limits, such as where the LPCO may be monitored to infer status and the HPCO status may be directly used with temperature and system mode state.