Mitsubishi Heavy Industries SRRM40HENG-L, Handbook, Page: 890 / 1106

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19.5.4 Refrigerant piping
(1) Precautions no refrigerant piping work for prevention against compressor lock
Compressor trouble including lock and motor burn-out is due to faulty parts but mainly concerned in installation and refrigerant
piping conditions, The precautions for refrigerant piping are as belows.
(a) Be sure to perform brazing while flowing nitrogen.
1) Without flowing nitrogen gas, a lot of oxide film (CU
2
O) is generated. In particular, in case of for building with many brazed
portions, oxide film is so much generated that this causes a fatal failure in the air conditioning system.
2) A foreign material (oxide film) causes clogging of the capillary tube or expansion valve, leading to non-cooling (non-
heating), abnormal discharge temperature, compressor lock due to a faulty oil return. In some cases, a lot of foreign materials
block the oil return hole of the accumulator, thereby causing a compressor lock. (This lock trouble may occur repeatedly 2 or
3 times.)
(b) Don’t admit water (waterdrops, condensation) into the piping.
1) Use a copper piping that is free from water (waterdrops,
condensation).
2) Don’t perform refrigerant piping work while it rains.
3) To suspend outdoor piping work, perform curing to prevent
water admission.
Bad effects of water
• Capillary tube and expansion valve clogging
• Refrigerant hydrolysis
→
“Acid” generation
→
Iron/copper corrosion
• Crystal foreign material (clathrate compound) genera-
tion resulting from reaction on refrigerating machine oil
(c) Don’t admit dust or foreign particles in the pipe.
Various foreign particles are included in air conditioners that caused trouble. Be careful about them.
(Concrete fragments, cement, sand, paint, metal powder (copper refuse after deburring, etc.), etc.
(d) Adopt the specified dimensions for pipes.
There will be directly conected to serious
trouble such as compressor lock or burn-
out of the compressor motor.
Too thick: Improper charge volume
Faulty oil return (insufficient gas flow rate)
Overcharge Liquid back
Compressor lock
Compressor lock
Faulty oil return
Too long (L):
(e) Be sure to support the refrigerant piping with support fittings.
1) The pipe vibrates and expands/shinks during operation. Without proper supports, a load is concentrated partially and cracks
and collapse occur on the piping, thereby causing a unit failure.
2) A support should be provided at intervals of 2 or 3 m so as not to partially concentrate a load.