System and method for identifying causes of hvac system faults

A method of operating heating, ventilation and air conditioning (HVAC) system, the method comprising:

• storing measurements of a suction-side property over an initial period of time, wherein the suction-side property is associated refrigerant provided to an inlet of a compressor of the HVAC system;
• detecting that a shutoff switch is tripped at a first time stamp corresponding to an end of the initial period of time, wherein the shutoff switch is configured to be tripped and automatically stop operation of the compressor and a fan of the HVAC system, in response to determining that a liquid-side property is greater than a predefined maximum value, wherein the liquid-side property associated with the refrigerant provided from an outlet of the compressor;
• accessing the measurements of the suction-side property;
• determining, based on the measurements of the suction-side property, whether the suction-side property has an increasing or decreasing trend;
• determining that a malfunction of the fan caused the shutoff switch to trip if the suction-side property has the increasing trend;
• and
• determining that a blockage of the refrigerant conduit subsystem caused the shutoff switch to trip if the suction-side property has the decreasing trend;
• wherein the suction-side property is a suction-side temperature of the refrigerant measured at a position proximate the inlet of the compressor and the liquid-side property is a liquid-side temperature of the refrigerant measured at a position proximate the outlet of the compressor.

A controller of heating, ventilation and air conditioning (HVAC) system, the controller comprising:

• an input/output interface configured communicatively couple the controller to:
• a shutoff switch configured to be tripped and automatically stop operation of a compressor and fan of the HVAC system, in response to determining that a liquid-side property is greater than a predefined maximum value, wherein the liquid-side property is associated with refrigerant provided from an outlet of the compressor;
• and
• a suction-side sensor positioned and configured to measure a suction-side property associated with the refrigerant provided to an inlet of the compressor;
• and
• a processor, coupled to the input/output interface, the processor configured to:
• store measurements of the suction-side property over an initial period of time;
• detect that the shutoff switch is tripped at a first time stamp corresponding to an end of the initial period of time;
• access the measurements of the suction-side property;
• determine, based on the measurements of the suction-side property, whether the suction-side property has an increasing or decreasing trend;
• determine that a malfunction of the fan caused the shutoff switch to trip if the suction-side property has the increasing trend;
• and
• determine that a blockage of the refrigerant conduit subsystem caused the shutoff switch to trip if the suction-side property has the decreasing trend;
• wherein the suction-side property is a suction-side temperature of the refrigerant measured at a position proximate the inlet of the compressor and the liquid-side property is a liquid-side temperature of the refrigerant measured at a position proximate the outlet of the compressor.