New R-32 split unit with poor cooling, an oil stain and no evacuation
A newly installed 1.5 TR inverter split air conditioner uses R-32 and a 5 m interconnecting pipe with a 3 m vertical rise. The manufacturer’s factory charge covers 5 m, so the installer adds no refrigerant. The unit is commissioned on a 35 °C day; indoor air is 27 °C dry-bulb and 19 °C wet-bulb. After 30 minutes the room remains warm, and the supply-air temperature is only 25 °C. The suction line is cool but not sweating, and the suction superheat is 20 K; liquid subcooling is 3 K. A faint oil stain is visible at the liquid-line flare at the outdoor unit. The installer had purged the lines with refrigerant and tightened the flares by feel, and did not use a vacuum pump or nitrogen pressure test. The condensate drain has a shallow trap and slopes toward the wall, where water drips. No error code appears. The customer demands that you simply add gas and leave.
1. Calculate the air temperature difference and interpret the superheat, subcooling and oil stain. Is this undercharge, a restriction, or an airflow problem?
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The air temperature difference is 27 - 25 = 2 K, which is far below the 8-12 K normally expected at these indoor conditions. The high superheat of 20 K and low subcooling of 3 K together point to a shortage of liquid refrigerant reaching the evaporator, or to a restriction. Airflow alone can reduce the temperature difference, but it would not normally produce high superheat with low subcooling.
The oil stain at the liquid-line flare is the decisive clue. A restriction would often show frost or condensation at the restriction and a large temperature drop across it, but it would not leave an oil trace at a flare. A new flare tightened by feel, with no nitrogen pressure test, is a likely leak point. The installer also purged with refrigerant instead of evacuating, so moisture and non-condensables may be present. Because the factory charge covers 5 m, the missing refrigerant is probably escaping rather than being omitted. Do not simply add gas; that would hide the leak and may overcharge the system.
2. Outline the repair and commissioning sequence you would use, including the safety requirements for R-32.
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First recover the remaining R-32 with a suitable recovery machine; do not vent it. R-32 is A2L, so remove ignition sources, ventilate the area, and use equipment rated for A2L refrigerant. Repair the flare properly: cut off the old flare, deburr, re-flare to the correct angle and length, and tighten with a calibrated torque wrench to the manufacturer's value. Replace the filter drier if moisture or debris is suspected.
Pressure-test with dry nitrogen at the manufacturer's test pressure and check every joint with soap solution or an electronic leak detector. Then evacuate with a vacuum pump and micron gauge to about 500 microns, isolate and hold to confirm no rise. Charge by weight according to the nameplate and pipe-length table; use liquid charging for R-32. Check superheat, subcooling, supply-air temperature difference, compressor current and drain operation. The shallow trap should be corrected to the manufacturer's trap dimensions and the drain given a continuous fall of at least about 1 in 50 so that water does not stand or drip at the wall.
3. How would you answer the customer who says ‘just add gas and leave’?
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Explain that adding gas without repairing the flare would leave the leak open. The unit would lose the added refrigerant again, and the customer would pay twice. Overcharging a leaking system can also raise discharge pressure and current, reduce cooling, and damage the compressor. The oil stain shows that refrigerant oil is already escaping, so the joint must be repaired and tested, not topped up.
Also explain that the unit was not evacuated or pressure-tested, so simply adding gas would not correct any moisture or non-condensable contamination. A proper repair, evacuation by weight and leak test takes longer but protects the warranty and the equipment. Offer a clear written quotation and a realistic completion time rather than promising a one-hour fix.