Abstract: An apparatus for the diagnosis of a cooling system which receives inputs in the form of data about a cooling system, and measurements made from the cooling system, and which then calculates the amount of refrigerant to be removed or added to the cooling system for optimal performance. In addition, methods for ensuring correct setup of a cooling system are disclosed. The methods may apply to FXV (fixed expansion valve) systems and may include making and displaying a prediction of a refrigerant adjustment based upon measurements such as return air wetbulb temperature, condenser air entering temperature, refrigerant superheat vapor line temperature, and refrigerant superheat vapor line pressure. A method for ensuring correct setup of a cooling system is disclosed.