provides an indication of the amount of charge in the system by suitably programming the controller 30 to recognize acceptable compressor suction superheat levels the controller 30 can then determine when it is necessary to adjust one or more of the expansion devices 50 to increase or decrease the amount of refrigerant within the active part of the system another approach for monitoring the refrigerant charge level in the active part of the system includes comparing the compressor discharge pressure with the refrigerant saturation pressure that corresponds to an indoor ambient temperature which may be obtained from the indoor unit 39 s air temperature sensor in this example approach the controller 30 is programmed to determine an overcharge condition when the discharge pressure from the compressor is excessively higher than the saturation pressure one aspect of the approach described in the previous paragraph is that it may include increasing the amount of refrigerant in the active part of the system when it appears that an undercharge situation exists the additional refrigerant may be added until a predetermined minimum difference between the actual compressor discharge pressure and the refrigerant saturation pressure is established the desired minimum difference between these pressures can be determined for various systems using testing or system simulation given this description those skilled in the art will be able to determine the appropriate minimum differences for particular system configurations another approach which is the currently most preferred approach is to monitor the superheat leaving the compressor of the outdoor unit 24 in this approach the actual temperature leaving the compressor is measured and the pressure leaving the compressor is determined one approach for determining the pressure leaving the compressor is to.