Refrigerant Recovery Control; Backup Control - Mitsubishi Electric PURY-M200YNW-A1 Service Handbook

[5-3 HBC Control ]
5-3-8

Refrigerant Recovery Control

The refrigerant recovery control function controls the refrigerant flow at the HBC during heating operation to keep the refrig-
erant from collecting inside the HBC.
It is also performed during cooling operation to prevent an excessive amount of refrigerant from accumulating in the outdoor
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.
Outdoor unit 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)
The opening of LEV1 and LEV2 on the HBC is increased.
5-3-9

Backup Control

The following backup control is started on the HBC as necessary.
(1) Backup mode for plate heat exchanger protection
The following control is performed depending on the outlet pipe temperature of the plate heat exchanger for freeze-up pro-
tection.
[Cooling-main/Heating-main operation]
1) Outdoor unit
Cooling-main operation: Continued; Heating-main operation: Continued
2) HBC
Outdoor unit Operation
mode
HBC 21S4Ma
21S4Mb
LEV1
LEV2
LEV3
SV1
PUMP1
PUMP2
VB3a~p
(2) Heating water temperature backup mode
When the heating operation can be continued without receiving heat from the refrigerant due to water temperature rise during
heating operation (the outlet pipe temperature of the plate heat exchanger is 70ºC or above), the outdoor unit goes into the
Thermo-OFF mode, and the heating operation is performed only by circulating the hot water by the water pump. When the
water temperature decreases to a certain level (the outlet temperature of the plate heat exchanger is 45ºC or below), the out-
door unit starts up.
BS_05_M
Cooling-main/Heating-main
Continues the current operation
Heating side: open (de-energized)
Cooling side: open (de-energized)
Maintains the opening that was used in the
previous operation mode
41 pulses: fully closed
3000 pulses: fully open
Closed
Continues the heating operation
Continues the cooling operation
The opening depending on the indoor unit
operation mode
Control mode
Cooling-only
Cooling-only Thermo-OFF
Cooling side: open (energized)
Cooling side: open (de-energized)
Opening during Cooling-only Thermo-OFF
Opening during Cooling-only Thermo-OFF
Opening during Cooling-only Thermo-OFF
Open
Continues the cooling-only operation
Continues the cooling-only operation
The opening depending on the indoor unit
operation mode
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chapter 5 -