Refrigerant Charging Process and Why Evacuation is Necessary

In refrigeration and air conditioning systems, it is essential to evacuate the system before refrigerant charging. This is because moisture and non-condensable gases can negatively affect the system's performance and cause premature failure.

Moisture in the system can form acidic sludge, leading to restrictions on expansion valves, evaporator coils, and reduced cooling efficiency. It can also cause deterioration of the insulation winding in hermetic compressors, resulting in a short circuit and compressor motor burnout.

Non-condensable gases, such as air, can enter the system during maintenance or repair, reducing cooling efficiency by limiting the amount of liquid refrigerant.

To evacuate the system, a vacuum pump and recovery bottle are used, and the pressure gauge is checked for 20-25 minutes to ensure that the system holds a negative pressure (vacuum), indicating that there are no leaks in the system.

Liquid refrigerant is added to the liquid line following proper conditions to avoid damage to the compressor. Vapor refrigerant is charged from the point where the system pressure is lower than the pressure in the charging cylinder. Charging from the discharge side of the compressor may result in refrigerant reversing, filling the charging cylinder instead of the system.

When moisture is present in the system, it combines with the refrigerant to form an acidic solution that dissolves copper tubing and extracts copper from copper-based alloys like brass or bronze. This copper plating can deposit in the compressor bearings and suction/discharge valves, causing leaks, reduced cooling efficiency, chocking of filters/driers, and contamination of refrigerant and oil.

The refrigerant charging process involves connecting hoses, gauges, and a temperature probe, evacuating the system into a recovery bottle, purging hoses, and charging the refrigerant from the refrigerant bottle to the low-pressure side of the system. The degree of superheat is monitored to ensure that the liquid is not entering the compressor suction. The pressure chart can calculate how much refrigerant is present in the system.

In conclusion, evacuating the system before refrigerant charging is necessary to ensure that moisture and non-condensable gases do not negatively affect the system's performance. Following the proper refrigerant charging process can help prevent damage and prolong the refrigeration system's lifespan.