LG Multi V Installation Manual page 12

Installation
Nitrogen substitution method
Welding, as when heating without nitrogen substitution a large amount of the oxide film is formed on the internal piping.
The oxide film is a caused by clogging EEV, Capillary, oil hole of accumulator and suction hole of oil pump in compressor.
It prevents normal operation of the compressor.
In order to avoid this problem, Welding should be done after replacing air by nitrogen gas.
When welding plumbing pipe, the work is required.
◆How to work
Oxide scale
Note) should not block the outlet side.
When the internal pressure in pipe is above the
atmospheric pressure, pinhole is occurred and it
is a leakage cause.
CAUTION :
1. Always use the nitrogen.(not use oxygen, carbon dioxide, and a Chevron gas):
Please use the following nitrogen pressure 0.02 MPa (2.9 psi)
Oxygen --------- Promotes oxidative degradation of refrigerant oil.
Because it is flammable, it is strictly prohibited to use
Carbon dioxide --- Degrade the drying characteristics of gas
Chevron Gas ---- Toxic gas occurs when exposed to direct flame.
2. Always use a pressure reducing valve.
3. Please do not use commercially available antioxidant.
The residual material seems to be the oxide scale is observed.
In fact, due to the organic acids generated by oxidation of the alcohol contained in the anti-oxidants, ants nest corrosion
occurs. (causes of organic acid → alcohol + copper + water + temperature)
12 Indoor Unit
Welding Point
(Should not
Regulator
Nitrogen gas Pressure
0.02 MPa (2.9 psi) less
Auxiliary valve
Taping
contain air)