Abstract: Apparatus for detecting low charge of a working fluid in a heat transfer system of the type having a fluid circuit comprising a compressor for pressurizing working fluid received from an evaporator, a condenser and condenser fan for cooling the working fluid received from the compressor, and an expansion device for controlling flow of the working fluid between the condenser and the evaporator, the apparatus comprising: a working fluid state sensor operative in response to a control signal and disposed in the fluid circuit on the outlet side of the evaporator to produce a working fluid state signal; and a control circuit for providing the control signal to the sensor and for controlling operation of the heat transfer system based on a comparison of the working fluid state signal with a state set point; the control circuit detecting a low charge condition of the working fluid when the state signal indicates the working fluid superheat exceeds a first predetermined threshold over a first predetermined time with

Abstract: Apparatus for detecting low charge of a working fluid in a heat transfer system of the type having a fluid circuit comprising a compressor for pressurizing working fluid received from an evaporator, a condenser and condenser fan for cooling the working fluid received from the compressor, and an expansion device for controlling flow of the working fluid between the condenser and the evaporator, the apparatus comprising: a working fluid state sensor operative in response to a control signal and disposed in the fluid circuit on the outlet side of the evaporator to produce a working fluid state signal; and a control circuit for providing the control signal to the sensor and for controlling operation of the heat transfer system based on a comparison of the working fluid state signal with a state set point; the control circuit detecting a low charge condition of the working fluid when the state signal indicates the working fluid superheat exceeds a first predetermined threshold over a first predetermined time with

Abstract: Apparatus for monitoring a refrigerant state in a refrigeration system includes a charge sensor and a controller. The sensor is positioned adjacent to the outlet of an evaporator. The sensor produces a voltage output signal in response to an input signal from the controller. The controller compares the output signal to a predetermined set point chosen to correspond to a predetermined refrigerant state. The sensor is preferably a self-heated thermistor positioned adjacent to flow exiting the evaporator through the outlet. The controller preferably compares the output signal to a set point at preset intervals and computes an average for a predetermined time duration. This helps to avoid false readings due to transitory conditions. The apparatus may be used in various types of refrigeration systems but is contemplated to be used primarily in mobile air conditioning systems in order to detect a reduced refrigerant charge in such systems.