Aux 2 Unit 9 Refrigerant Under/ re-charge, leaks, trouble shooting Q6 Answer

Describe, with the aid of a sketch, the procedure for Liquid Charging refrigeration plant stating all safety procedures and checks to be carried out. (10)

Preparation & Safety Checks
- Ensure the correct refrigerant type and cylinder are available and properly labelled.
- Confirm the plant has been leak-tested and evacuated to the required vacuum before charging.
- Verify the charging manifold, hoses, and valves are in good condition and compatible with the refrigerant.
- Wear correct PPE (gloves, goggles, protective clothing) to prevent frostbite or chemical burns.
- Ensure adequate ventilation in the charging area to avoid accumulation of refrigerant vapour.
- Prohibit naked flames, smoking, or sources of ignition.

Cylinder Position and Connection
- Place the refrigerant cylinder on a weighing scale (to measure the mass charged).
- Keep the cylinder upright when vapour charging; for liquid charging, invert the cylinder so that liquid refrigerant is withdrawn.
- Connect the cylinder to the charging port (usually on the liquid line between condenser and expansion valve) using a manifold gauge set and charging hose.
- Purge air from hoses by slightly loosening connections until refrigerant vapour displaces the air.

Charging Procedure
- Open the cylinder and manifold valves slowly to allow liquid refrigerant into the system.
- Charge initially into the high-pressure side (liquid line) when the plant is idle, or into the receiver if fitted.
- Start the compressor and continue charging slowly, monitoring suction and discharge pressures, sight glass, and temperature readings.
- Control the charging rate carefully to avoid liquid slugging into the compressor.
- Use the sight glass in the liquid line (if fitted) to judge when the system is fully charged (clear liquid flow with no bubbles).

Completion
- Close the manifold and cylinder valves when the correct charge (by weight or condition) is reached.
- Disconnect hoses carefully, ensuring any trapped refrigerant is safely vented to recovery equipment (not to atmosphere, in compliance with MARPOL and F-gas regulations).
- Replace service port caps tightly to prevent leakage.
- Record the amount of refrigerant added in the log book for maintenance and statutory records.