Mitsubishi Electric PQHY-P72ZLMU-A Service Handbook page 157

[ VII Control ]
-7- Refrigerant Recovery Control <PQHY>
Recovery of refrigerant is performed during heating operation to prevent the refrigerant from accumulating inside the unit while
it is stopped (unit in fan mode), or inside the indoor unit that is in cooling mode or in heating mode with thermo off. It is also
performed during cooling operation to prevent an excessive amount of refrigerant from accumulating in the heat source heat
exchanger.
(1) During heating operation
Starting refrigerant recovery mode
The refrigerant recovery mode in heating starts when all of the following three conditions are met:
15 minutes have passed since the completion of previous refrigerant recovery.
TH4 > 115°C [239°F]
Frequencies below 50 Hz
Refrigerant recovery
1) Refrigerant is recovered with the LEV on the applicable indoor unit (unit under stopping mode, fan mode, cooling, heating with
thermo off) being opened for 30 seconds.
2) Periodic capacity control of the heat source units and periodic LEV control of the indoor units will be suspended during refrig-
erant recovery operation; they will be performed after the recovery has been completed.
(2) During cooling operation
Starting refrigerant recovery mode
The refrigerant recovery mode starts when all the following conditions are met:
30 minutes have passed since the completion of previous refrigerant recovery.
When the unit keeps running for 3 minutes in a row or more with high discharge temperature
TH4 > 105°C [221°F] or 63HS1 > 3.43 MPa [497 psi] (35 kg/cm
Refrigerant recovery
The opening of LEV1 is increased and periodic control begins again.
-8- Refrigerant Recovery Control <PQRY>
Refrigerant recovery is performed for each BC port during heating operation to prevent the refrigerant from accumulating in-
side the units that are stopped (in the fan mode), in the cooling mode, or in the heating Thermo-OFF mode.
It is also performed during cooling operation to prevent an excessive amount of refrigerant from accumulating in the heat
source heat exchanger.
Starting criteria for the refrigerant recovery cycle (during Cooling-only, Cooling-main, Heating-only, or Heating-main
mode)
The refrigerant recovery mode starts when all of the following conditions are met:
1) When 5 minutes have passed in the Heating-only or Heating-main mode or 30 seconds have passed in the Cooling-only or
Cooling-main mode since the completion of the previous refrigerant recovery cycle AND the when following conditions are
met.
TH4 > 105°C [221°F]
2) When the port is not in the 4-minute restart delay mode
Starting criteria for the refrigerant recovery cycle (during Cooling-only, Cooling-main, Heating-only, or Heating-main
mode)
1) When the port is in the cooling Thermo-OFF, fan, or stop mode
SV C at the port turns on for 30 seconds. (
2) The opening of LEV1 and LEV3 is increased.
-9- Capacity Control of Heat Exchanger<PQHY>
(1) Control method
Depending on the capacity required, the heat exchanger capacity of the heat source unit is controlled by the solenoid valve
and LEV to keep a constant condensing temperature of (water temperature +10°C [50°F]) during cooling operation and a con-
stant evaporation temperature of (4°C [39°F] =0.80 <Pa [116psi]) during heating operation.
The OS in the multiple-heat source-unit system operates at the actual heat exchanger capacity control value that is calculated
by the OS based on the preliminary heat exchanger capacity control value that the OC determines.
HWE15150
Opening of LEV during refrigerant recovery
Opening of indoor unit LEV: 400 pulses
Initial opening of LEV
indicates port No.)
30 seconds
Start
Finish
2
G) and SC0 > 10°C [18°F]
- 148 -
GB