Mitsubishi Electric CITY MULTI PUHY-400YMF-C Service Handbook page 98

(5) Oil return control (Electronic expansion valve (SLEV); Variable Capacity Unit only)
• 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 (Variable capacity unit), 46 to 300 (Constant capacity unit).
(7) Defrosting control
Defrosting operation controls vary depending on the state of operations before defrosting begins.
State of operations
before defrosting
Defrosting
oper ation control
*1 When the cumulative operating time of the constant capacity unit compressor
*2 When the cumulative operating time of the constant capacity unit compressor < 30 minutes.
1) Start of defrosting
1 1 2
Defrost 1 - ,
• After there has been heating operation for 50 minutes and a piping temperature (TH5) of 0˚C or less is detected for
a preset time in either the variable or constant capacity units, defrosting starts.
2
Defrost 2
• After there has been heating operation for 50 minutes, and a piping temperature of (TH5) of 0˚C or less is
detected for a preset time in the variable capacity unit, defrosting starts.
3
Forced Defrosting
• 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 (DIPSW2-7) to ON starts forced defrosting.
2) End of Defrosting
1 1 2
Defrost 1 - ,
• Defrosting ends when 15 minutes has passed since the start of defrosting or when the piping temperature (TH5)
of both the variable and constant capacity units becomes 7˚C or more.
2
Defrost 2
• Defrosting ends when 15 minutes has passed since the start of defrosting or when the piping temperature (TH5)
of the variable capacity unit becomes 8˚C or more.
* Ending the defrosting is prohibited for 2 minutes after the start of defrosting. (Note that the defrosting operation will
be stopped if the piping temperature exceeds 20˚C or if the high pressure (Pd) exceeds 1.96 MPa.)
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.
Variable capacity unit
Constant capacity unit
Variable capacity unit
Constant capacity unit
Indoor unit LEV
1
Defrost 1 - Defrost 1 -
Operating Operating
Operating Stopped
Defrost Defrost
Defrost Defrost *1
Full open
-95-
2
Defrost 2
Operating
Stopped
Defrost
Stopped *2
Full closed
30 minutes.