second releasable connector 27 a is connected to high pressure conduit or so called liquid line 20 but may be connected to conduit 18 alternatively connector 27 a includes a schrader valve 27 c conduit 18 is connected to the so called high pressure side of compressor 16 for conducting heated vapor to heat exchanger 14 for at least partial condensation therein and then discharge to conduit 20 accordingly working fluid flowing out of the heat exchanger 14 through conduit 20 to expansion device 22 is typically in liquid form and the pressure and temperature of such fluid may be sensed by respective temperature and pressure sensors 40 and 42 as shown in fig1 sensors 40 and 42 may include direct readout displays or gauges 40 a and 42 a and are operatively connected to a further controller unit or circuit 44 which may be operably connected to the controller unit 28 to receive power therefrom and deliver certain control signals thereto controller 44 may be a suitable programmable microcontroller or an application specific integrated circuit previously programmed for operation in accordance with the invention controller 44 includes a part 45 including visual indicators 46 and 48 for indicating the status of a refrigerant or working fluid charge in the system 10 a visual display 48 a may also be provided for displaying information to a user the controller part 45 is also adapted to provide an electric output signal to conductor means 50 which may be releasably connected to the controller part.