What needs to be checked before adding refrigerant to a VRF air conditioning system?
Before adding refrigerant to a VRF air conditioning system, the following six categories of checks must be completed to ensure the system operates safely and in accordance with regulations:
I. Piping System Integrity Inspection
Verify pipe specifications: Compare the pipe size chart provided by the manufacturer to confirm that the diameter and length of the gas and liquid pipes match.
Branch pipe orientation: Confirm that all branch pipes (BS boxes, BE boxes) are installed in the correct orientation, with no reverse or inverted installations.
Insulation integrity: All pipe, branch pipe, and valve connections have completed insulation layer construction with no exposed areas.
II. Air tightness test (pressure holding and leak detection)
Nitrogen pressurization: Slowly pressurize with dry nitrogen to the specified pressure (approximately 3.8 MPa 550 psi for R410A systems).
Pressure holding time: Hold pressure for at least 24 hours, and observe pressure changes.
Temperature correction: The pressure reading is corrected according to changes in ambient temperature to eliminate temperature interference.
Leakage detection: When the pressure drops, use a halogen leak detector or soapy water to check for leaks. After repair, re-pressurize.
III. Vacuum drying (vacuum extraction)
Vacuum pump evacuation: Use a vacuum pump to simultaneously evacuate from both high and low pressure sides.
Vacuum requirement: ≤-0.1MPa (approximately 755mmHg) and maintained for a sufficient time.
Confirming the absence of moisture: Vacuuming is a crucial step in removing air and moisture from the system to prevent ice blockage, system contamination, and compressor damage.
IV. Electrical Safety Inspection
Power supply voltage: Confirm that the power supply voltage meets the requirements of the outdoor unit's nameplate.
Communication line polarity: Confirm that the communication lines between the indoor and outdoor units are connected correctly (most VRF air conditioning systems are polarity sensitive).
Grounding continuity: All indoor and outdoor units are reliably grounded, and the grounding resistance meets the specifications.
V. Refrigerant and Equipment Validation
Refrigerant type: Confirm the use of the specified type (R410A, R32, etc.). Mixing different refrigerants is strictly prohibited.
Total pipe length calculation: Calculate the additional refrigerant charge based on the actual pipe length.
Number of indoor units: Confirm that the number of indoor units configured in the system is consistent with the design.
VI. Safety Protection and Tool Inspection
Personal protective equipment: Wear goggles, frostbite-resistant gloves, and protective clothing (splashes of liquid refrigerant can cause frostbite).
Tools in good working order: Confirm that the pressure gauge set, connecting hoses, and refrigerant charging hose are leak-free and show no signs of aging.
Good ventilation: The work area should be well-ventilated to prevent refrigerant buildup and oxygen deficiency.
Core principle: Refrigerant charging of VRF air conditioning systems can only be carried out after all three prerequisites—dryness, cleanliness, and airtightness—have been met. Charging refrigerant directly without pressure testing, leak detection, and vacuuming is the most common cause of compressor damage and system ice blockage.
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