Avoiding coil freeze in HVAC systems

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

• monitoring a property value measured by a sensor, the sensor configured to measure a property value associated with saturated refrigerant flowing through an evaporator;
• detecting a system fault, based on the monitored property value;
• and
• in response to detecting the system fault, operate a variable-speed compressor of the HVAC system in a freeze-prevention mode, the freeze-prevention mode configured to maintain the monitored property value above a setpoint value by adjusting a speed of the variable-speed compressor.

A controller for operating a heating, ventilation, and air conditioning (HVAC) system, the controller comprising:

• a memory configured to store a setpoint value associated with operating the HVAC system in a freeze-prevention mode;
• an input/output interface configured to:
• receive measurement data from a sensor, the configured to measure a property value associated with saturated refrigerant flowing through the evaporator;
• and
• transmit a control signal to a variable-speed compressor of the HVAC system;
• and
• a processor coupled to the memory and the input/output interface, the processor configured to:
• monitor the property value measured by the sensor;
• detect a system fault, based on the monitored property value;
• and
• in response to detecting the system fault, cause the input/output interface to transmit the control signal, the control signal instructing the variable-speed compressor to operate in the freeze-prevention mode, the freeze-prevention mode configured to maintain the monitored property value above the setpoint value by adjusting a speed of the variable-speed compressor.