6 Special Control - Midea M-Thermal Series Service Manual

6 Special Control
6.1 Oil Return Operation
In order to prevent the compressor from running out of oil, the oil return operation is conducted to recover oil that has
flowed out of the compressor and into the refrigerant piping. When the oil return operation is being conducted, the
outdoor unit refrigerant system main PCB displays code d0.
The oil return operation starts when the following condition occurs:
 When the compressor cumulative operating time with running rotation speed less than 42rps reaches 6 hours.
The oil return operation ceases when any one of the following three conditions occurs:
 Oil return operation duration reaches 5 minutes.
 Compressor stops.
Tables 3‐6.1 show component control during oil return operation in cooling mode.
Component
Inverter compressor
DC fan motor
Electronic expansion valve
Four‐way valve
Tables 3‐6.2 show component control during oil return operation in heating and DHW modes.
Component
Inverter compressor
DC fan motor
Electronic expansion valve
Four‐way valve
6.2 Defrosting Operation
In order to recover heating capacity, the defrosting operation is conducted when the outdoor unit air side heat exchanger
is performing as a condenser. The defrosting operation is controlled according to outdoor ambient temperature, air side
heat exchanger refrigerant outlet temperature and the compressor running time.
Table 3‐6.3: Component control during defrosting operation
Component
Inverter compressor
DC fan motor
Electronic expansion valve
Four‐way valve
6.3 Force Cooling Operation
The force cooling operation helps the refrigerant recovering before removal the water side heat exchanger.
The force cool mode can be ended by pushing the button on the outdoor refrigerant system main PCB named "force‐cool"
for 5s or this mode will be ended automatic if the system has operated force cool mode for more than 30 minutes.
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Wiring diagram
4‐10kW
label
COMP
●
FAN
●
EXV
●
4‐WAY
●
Wiring diagram
4‐10kW
label
COMP
●
FAN
●
EXV
●
4‐WAY
●
Wiring diagram
4‐10kW
label
COMP
●
FAN
●
EXV
●
4‐WAY
●
Midea CAC Confidential
M‐Thermal Split
Control functions and states
Runs at oil return operation rotation speed
Controlled according to cooling mode
304 (steps)
Off
Control functions and states
Runs at oil return operation rotation speed
Controlled according to heating mode
304 (steps)
On
Control functions and states
Runs at defrosting operation rotation speed
Off
Fully open
Off