Abstract: An HVAC system includes an evaporator coil and a compressor fluidly coupled to the evaporator coil. A condenser coil is fluidly coupled to the compressor. The condenser coil includes at least one condenser circuit fluidly coupled between a discharge line and an exit manifold. A sub-cool circuit is fluidly coupled between the exit manifold and a liquid line. A first temperature sensor is disposed at an entrance to the sub-cool circuit. A second temperature sensor is disposed at an exit to the sub-cool circuit. An HVAC controller is operatively coupled to the first temperature sensor and the second temperature sensor. The HVAC controller is configured to determine a temperature difference across the sub-cool circuit.