Equipment installation and piping work
1. Placing the units
- Indoor unit: high on a strong wall (about 2.3 m or more above the floor), with space above and on the sides for air, away from heat sources, and where cold air will spread across the room.
- Outdoor unit: on a firm, level stand or wall bracket, in shade if possible, with free space on the air-inlet and air-outlet sides so hot air does not go back in.
2. Refrigerant piping
- Two copper pipes: a thin liquid line and a thick gas (suction) line.
- Use clean, dry copper made for refrigeration. Cut square, remove burrs and keep the ends closed so dirt and moisture do not enter.
- Join with flare nuts (tighten to the torque the maker gives) or with brazing while a little nitrogen flows through the pipe.
- Insulate both pipes (at least the gas pipe) so they do not sweat or lose cooling.
- Keep the pipe short, with few bends, and follow the maximum length and height difference in the manual. For long pipes some extra refrigerant is added.
3. Drain pipe
Water taken from the air must leave. Slope the drain downward at least 1 cm per metre (1:100) with no dips. Do not join it into a sewer without a trap or air break.
4. Power and control
A separate circuit with the right breaker and thick enough cable, earthing and a switch near the outdoor unit.
Testing, inspecting and maintaining air-conditioning
Leak test
Fill the pipes with dry nitrogen (not air, not oxygen) to the pressure the maker states. Watch the gauge for several minutes or hours. A steady gauge means no leak. A falling gauge means a leak: check joints with soapy water (bubbles show the leak). Remember that the gauge also changes a little with room temperature, because gas pressure rises and falls with temperature.
Vacuum
Air and moisture inside would freeze, form acid and damage the compressor. A vacuum pump pulls the pipes down to a deep vacuum (gauge near −100 kPa, or a few hundred microns). Close the pump and wait 15 to 30 minutes: the vacuum must hold. Then open the outdoor valves to let the refrigerant in.
Commissioning (first run)
- Check the unit runs and the fan turns the right way.
- Measure the air entering and leaving the indoor unit. The difference is typically 8 to 12 °C.
- Check the running current against the nameplate, check the pressure and listen for noise.
- See water leave the drain pipe.
Maintenance
- Clean filters every month or two (a dirty filter blocks air and cuts cooling).
- Clean the indoor and outdoor coils once or twice a year.
- Check drain, electrical joints, insulation and refrigerant level; record readings in a log.
- Only trained people should handle refrigerant. Never release it into the air.
Key formulas and definitions
- Drain drop = length × slope (for 1:100, drop = length ÷ 100)
- Cooling by air: Q = airflow × 1.2 kg/m³ × 1.005 kJ/kg·K × ΔT
- Gas pressure ∝ absolute temperature (P₁/T₁ = P₂/T₂, T in kelvin)
- Extra charge = (pipe length − free length) × grams per metre
- Normal ΔT across indoor unit: about 8 to 12 °C
Worked examples
1. A drain pipe is 6 m long and must slope 1:100. How much lower is the outlet end?
Drop = 6 m ÷ 100 = 0.06 m = 6 cm.
2. The nitrogen gauge shows 1000 kPa (treat as absolute) at 27 °C. By night it cools to 12 °C. What does the gauge show if there is no leak?
T₁ = 300 K, T₂ = 285 K. P₂ = 1000 × 285 ÷ 300 = 950 kPa. So a small fall may just be the temperature, not a leak. Re-check at the same temperature.
3. Return air is 27 °C and supply air is 17 °C. Is the unit working normally?
ΔT = 27 − 17 = 10 °C, which is in the normal 8 to 12 °C range. Yes.
4. The indoor unit moves 0.15 m³/s of air with ΔT = 10 °C. Find the cooling in kW.
Q = 0.15 × 1.2 × 1.005 × 10 = 1.81 kW (sensible cooling).
5. A unit has 5 m of pipe free of extra charge and needs 20 g per extra metre. The installed pipe is 12 m. How much extra refrigerant?
Extra length = 12 − 5 = 7 m. Extra charge = 7 × 20 = 140 g.
Common mistakes
- Testing with air or oxygen. Use dry nitrogen only.
- Skipping the vacuum. Moisture and air stay in and damage the compressor.
- A flat or dipping drain pipe. Water pools, leaks into the room or breeds germs.
- Judging a leak without thinking about temperature. A cold night alone can drop the gauge a bit.