In a conventional refrigeration system, one of the most common problems occurs because of improper refrigerant charge. Although the proper amount of refrigerant may be readily determined by checking the pressure and temperature of liquid from the condenser, many service technicians just don't use this method, and frequently have their own personal methods.
The variety of methods used is unknown, but there are a number of them. The difficulty with each one is that none of them will give the precise charge amount of refrigerant required.