Mitsubishi Electric CITY MULTI PUHY-400YMF-B, Service Handbook, Page: 65 / 204

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(5) Oil return control (Electronic expansion valve (SLEV))
• The amount of opening of the oil-return LEV (SLEV) is determined as follows: in cooling, by the operating capacity
of the No. 1 compressor and the ambient temperature; in heating, by the operating capacity of the No. 1 compressor.
• It is opened (64) when both compressors are stopped and started for 10 minutes. (Upper limit of LEV opening is So
= 388 pulse.)
• SLEV = 0 when the No. 1 compressor is stopped.
(6) Sub-cool coil control (Electronic expansion valve (LEV1))
• The sub-cool coil control provides control every 30 seconds to keep the super heat volume from the temperature of
the inlet/outlet of the sub-cool coil (TH8, TH9) within a stable range (2 to 4 degrees).
• It controls by correcting the amount of opening according to the temperature of the inlet/outlet of the sub-cool coil
(TH5, TH7), the high pressure (Pd) and discharge temperature.
• It is closed (0) in heating or when the compressor is stopped.
• It has a fixed opening (480) in defrosting.
• During normal control, the operating range is 46 to 480.
(7) Defrosting control
1) Start of defrosting
• After there has been heating operation for 50 minutes or after 90 minutes has passed and a piping temperature
(TH5) of – 8
°
C or less is detected for a preset time, defrosting begins.
• When 10 minutes has passed since the compressor began operation or if 10 minutes has passed since recovery
from defrosting, setting the forced defrosting switch (Dip SW2-7) to starts forced defrosting.
2) End of defrosting
• Defrosting ends when 15 minutes have passed since the start of defrosting, or when a piping temperature (TH5) of
7
°
C or more is detected for 2 minutes or longer. (Note that if the defrost-prohibited time is set on 90 minutes, the
defrost-prohibit time will be 50 minutes following a 15-minute timed recovery.
• Ending the defrosting is prohibited for 2 minutes after the start of defrosting. (Note that the defrosting operation will
be ended if the piping temperature exceeds 20
°
C within 2 minutes of the start of defrosting.
3) Defrost-prohibit
• Defrosting is not performed for 10 minutes after the start of compressor operation and during oil recovery mode.
4) Abnormalities during defrosting
• If an error is detected during defrosting, the defrosting is stopped and the defrost-prohibit time is set to 20 minutes
by the compressor cumulative operating time.