Refrigerant may be added to a system in either a vapor (gas) or liquid state. Both saturated vapor and liquid refrigerant exist in a refrigerant cylinder. Vaporized refrigerant is at the top of the cylinder and liquid refrigerant is at the bottom. The method used to charge refrigerant depends on the type of cylinder being used. If using a disposable cylinder, the cylinder must be set in the upright position in order to charge with vapor (Figure SP-4-2). To charge liquid refrigerant into the system, the cylinder must be turned upside down.
Cylinders normally used with recovery or recycle units remain in the upright position when charging. They have valves that are used to select either vapor or liquid refrigerant for charging (Figure SP-4-3).
