Mitsubishi Electric CITY MULTI PUHY-HP-TJMU-A Instruction Manual page 9

Precautions for outdoor unit combinations
Refer to [Fig. 9.2.2] for the positioning of twinning pipes.
[Fig. 9.2.2]
<A> Install the piping so that oil will not accumulate in the stopped outdoor unit.
Unit 1 Unit 2
1.
C
F
The NG example shows that oil accumulates because the units are installed on a reverse gradient while unit 1 is in operation, and unit 3 is stopped.
Unit 1 Unit 2
2.
Unit 1 Unit 2
h1
h1 = 0.2 m (7-7/8 in) max
The NG example shows that oil accumulates into units 1 and 2 while unit 3 is in operation, and units 1 and 2 are stopped. Vertical pipe height (h) should be 0.2 m (7-7/8 in) or below.
Unit 2
Unit 1
3.
h1 h2
h2 = 0.1 m (3-15/16 in) max
h1 = 0.2 m (7-7/8 in) max
The NG example shows that oil accumulates into unit 1 while unit 3 is in operation, and unit 1 is stopped. Vertical pipe height (h) should be 0.2 m (7-7/8 in) or below.
Unit 1 Unit 2
4.
h2 = 0.1 m (3-15/16 in) max
h1 = 0.2 m (7-7/8 in) max
The NG example shows that oil accumulates into unit 3 while unit 1 is in operation, and unit 3 is stopped. Vertical pipe height (h) should be 0.2 m (7-7/8 in) or below.
<B> When the piping on the outdoor unit side (from the twinning pipe) exceeds 2 m [6 ft], ensure a trap (gas pipe only) within 2 m [6 ft].
Make sure the height of the trap is 200 mm [7-7/8 in] or more.
If there is no trap, oil can accumulate inside the pipe, causing a shortage of oil and may damage the compressor.
2 m ( 6 ft )
Caution:
• Do not install traps other than the ones between outdoor units described on a separate sheet to prevent oil backflow and compressor start-up failure.
• Do not install solenoid valves to prevent oil backflow and compressor start-up failure.
• Do not install a sight glass because it may show improper refrigerant flow.
If a sight glass is installed, inexperienced technicians that use the glass may overcharge the refrigerant.
Unit 3
A
F
Unit 3
Unit 3
Unit 3
Unit 3
h2
h1
F
C
Unit 1 Unit 2
C
F
F
Unit 1 Unit 2
h1
h1 > 0.2 m (7-7/8 in)
Unit 2
Unit 1
h1 h2
h2 > 0.1 m (3-15/16 in)
h1 > 0.2 m (7-7/8 in)
Unit 1 Unit 2
h2 h1
h2 > 0.1 m (3-15/16 in)
h1 > 0.2 m (7-7/8 in)
D
F
E
Unit 3
B
Unit 3
Unit 3
Unit 3
C
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