A further check on the refrigerant charge is described on pages 33 8. When vapour charging a system with an azeotropic refrigerant such as R502 the refrigerant cylinder must always be kept in a vertical position to prevent the possibility of liquid refrigerant from entering the compressor. This can create a dynamic pressure when the compressor starts, causing damage to valves or may even break piston connecting rods and damage pistons. The liquid refrigerant will also flush lubricating oil from bearing surfaces. The main disadvantage of vapour charging to the low side of the system is that it is a comparatively slow process, especially during low ambient temper- ature.
