Mitsubishi Electric CITY MULTI PUHY-400YMF-B Service Handbook page 89

(12) Refrigerant recovery control
Refrigerant recovery is conducted to prevent refrigerant from accumulating in the stopped unit (fan unit), the unit under
cooling mode and that with heating thermostat being turned off.
1) Start of refrigerant recovery
1 Refrigerant recovery is started when the two items below are fully satisfied.
• 30 minutes has passed after finishing refrigerant recovery.
• The variable capacity unit level detector or the constant capacity unit level detector detects AL = 0 for 3 minutes
continuously, or the discharge SH is high.
2) Refrigerant recovery operation
• Refrigerant is recovered by opening LEV of the objective indoor units (indoor units under stop. fan, and cooling
modes, and that with heating thermostat being turned off) for 30 seconds.
LEV opening at refrigerant recovery
(Indoor unit LEV opening 500 pulse)
• The regular capacity control of the outdoor unit and the regular LEV control of the indoor unit are not applied during
refrigerant recovery operation, but are fixed with the value before the recovery operation. These controls will be
conducted one minute after finishing the recovery operation.
• Defrosting operation is prohibited during the recovery operation, and it will be conducted after finishing the recovery
operation.
(13) Outdoor unit heat exchanger capacity control
Variable capacity unit
1) Control method
• In order to stabilize the evaporation temperature during cooling and the high-pressure pressure during heating that are
required in response to performance needs, the capacity of the outdoor heat exchanger is controlled by regulating the
fan volume of the outdoor unit by phase control and controlling the number of fans and by using the solenoid valves.
2) Control
• When both of the compressors are stopped, the fans for the outdoor units are also stopped.
• The fans operate at full speed for 10 seconds after starting.
• The fans for the outdoor unit are stopped during defrosting.
3) Capacity control pattern
Operating mode Capacity control pattern Heat exchanger capacity No. of fans Phase control
Cooling
Heating
Defrosting
Note 1: When there is conductivity at SV5b, it is open. When there is no conductivity at SV5b, it is closed.
Note 2: When the unit is stopped, and SV5b are open.
Note 3: When the unit is stopped, there is no conductivity at 21S4b, in cooling mode and SV5b is opened.
Constant capacity unit
1) Control Method
• In response to performance needs, the fan level is controlled by the same phase control used in the variable
capacity unit.
2) Control
• The fan is stopped when the (constant capacity unit) compressor is stopped.
• The fan is operated at full speed for 5 seconds after the (constant capacity unit) compressor is started.
• The fan for the outdoor unit is stopped during defrosting.
• The fan is sometimes operated when the TH10a drops, even when the compressor is stopped.
• The fan is operated for several minutes after the compressor is stopped.
LEV opening
before change
Starts
1 50 %
2 100 %
1
100 %
1 100 %
30 seconds
Finish
1 10 to 100 %
2 10 to 100 %
2 10 to 100
0 0
–86–
Notes
21S4bON
SV5bON
21S4bOFF
SV5bOFF
21S4bON
%
SV5bOFF
21S4bOFF
%
SV5bOFF