What is the professional process for repairing a refrigerant leak and recharging an inverter AC?

Repairing a refrigerant leak and recharging an inverter AC requires specialized tools and strict adherence to HVAC procedures. Inverter systems are particularly sensitive to precise gas charging because they use variable-speed compressors and electronic expansion valves (EEVs).

Step-by-Step Professional Repair & Recharge Process

1

Pressure Testing & Leak Detection

Locating the point of loss

1. Refrigerant Recovery: Any remaining gas in the system is recovered into a recovery cylinder using an HVAC recovery machine.
2. Dry Nitrogen Pressurization: The technician pressurizes the copper lines and coils with dry nitrogen gas (typically up to 350–450 PSI depending on R410A/R32 specifications).
3. Leak Isolation: The technician uses an electronic leak detector, ultrasonic sensor, or soap bubble solution to identify micro-leaks at flare nuts, brazed copper joints, or coil bends.

2

Structural Leak Repair

Sealing the system

1. Flare Nut Repair: If the leak is at a brass valve connection, the old flared pipe end is cut off, re-reamed, and a fresh precision flare is made using a flaring tool before torquing to specification.
2. Brazing Copper Tubing: If the leak is in a copper pipe or heat exchanger coil, the technician performs silver brazing using an oxy-acetylene torch while purging nitrogen through the pipe to prevent internal oxidation (scale buildup).

3

Evacuation & Deep Vacuum

Removing moisture and non-condensables

1. A two-stage rotary vacuum pump is connected to the service ports via a manifold gauge set.
2. The system is pulled down to a deep vacuum of under 500 microns.
3. Micron Hold Test: The vacuum pump is isolated, and the gauge is monitored for 15–30 minutes. If the vacuum holds steady, it confirms the system is sealed and entirely free of moisture and air.

4

Weigh-In Refrigerant Recharge

Critical precision step

1. Charging by Weight Only: Inverter ACs cannot be accurately charged by pressure alone due to variable compressor speeds. The technician uses a digital refrigerant scale to measure the exact factory charge listed on the outdoor unit’s data plate (e.g., 850 grams of R32 or R410A).
2. Liquid-Phase Charging: The refrigerant cylinder is inverted (if using blended gases like R410A) to charge pure liquid into the high-pressure side or liquid line while the system is off.

5

Performance & Current Testing

Operational verification

1. Superheat/Subcooling Verification: The AC is turned on, and temperatures across the suction and liquid lines are monitored alongside ambient room conditions.
2. Ampere & Frequency Check: Using a clamp meter, the technician verifies that the running current matches factory specifications as the inverter PCB ramps up the compressor frequency.

Key Requirements for Modern Refrigerants (R32 / R410A)

• No Top-Ups on Blended Gases (R410A): If an R410A system loses gas, the fractional mixture of R32 and R125 becomes unbalanced. The remaining gas must be completely evacuated and fresh refrigerant weighed in.
• Flammability Precautions (R32): R32 is a mildly flammable (A2L) refrigerant. Vacuum evacuation and nitrogen purging are mandatory to ensure no oxygen remains inside the system prior to operation.