This article will address the question: How much refrigerant, ammonia or halocarbon (Freon®), does your system need in order to operate properly? The simple answer - just enough to ensure that the High Pressure Liquid line leaving the High Pressure Receiver is immersed in liquid and is not drawing vapor.

Most complex systems have one or more sight glasses or “bulls eyes” installed in the High Pressure Receiver that will indicate the level of liquid in the vessel. Check the liquid level in the receiver when the refrigeration system is operating at or near maximum capacity; this is when the refrigerant usage will be the greatest. When the system is running with a good load the liquid level in the High Pressure Receiver needs to cover the outlet connection of the liquid line piping. On horizontal receivers with the liquid outlet connection on the top of the vessel, the receiver will have an internal pipe that draws the liquid from bottom of the vessel. The liquid level only needs to be a few inches or a few percent above this level. The remaining volume in the receiver is vapor and provides storage space for liquid when the system load decreases or the system is pumped down for maintenance.

Some systems do not have a means to view the liquid level directly in the High Pressure Receiver. In these systems a sight glass is generally installed in the liquid line near the outlet of the receiver. When the system is operating with a reasonably heavy load this sight glass should show a solid column of pure refrigerant liquid. Stated another way, the liquid line sight glass should not have vapor bubbles in the refrigerant stream.

Many complex halocarbon systems utilize “head pressure controls” to help maintain proper operating pressures, particularly during the winter months. These controls will require that the condenser be partially filled with liquid during the cold months. This extra liquid will show up in the High Pressure Receiver on warmer days so don’t be surprised to see the liquid level changing as the ambient temperature swings from cold to warm.

In summary, your refrigeration system needs to have enough refrigerant to make it operate properly under all conditions, but there is no reason to carry more than is necessary.