Defrosting Operation; Reverse Cycle Defrosting Operation - Midea VRF Series Service Manual

7.2 Defrosting Operation

In order to recover heating capacity, the defrosting operation is conducted when the outdoor unit heat exchanger is
performing as an evaporator. The defrosting operation is controlled according to outdoor ambient temperature, outdoor
heat exchanger temperature, indoor heat exchanger temperature and outdoor units running time. When the outdoor unit
is running in defrosting, the digital display on outdoor main PCB will display "df".

Reverse Cycle Defrosting Operation

Timing of reverse cycle defrosting operation:

Te<-2°C and T4<20°C, meeting either of the points below:
1) When there is an obviously drop in the temperature of outdoor unit heat exchanger outlet
2) When cumulative operating time after the latest defrosting control arrives an hour

Compulsive defrosting or oil return set manually after PI control 1min. (Set n17 by "SW5" in main board or spot check
board)
Table 3-7.3: Outdoor unit and MS component control during defrosting operation
Component
Inverter
compressor A
Inverter fan 1
Inverter fan 2
Four way valve
ODU
Electronic
expansion valve
Solenoid valve
Electric ball
valve
MS01
Electronic
expansion valve
Solenoid valve
MS04-12
Electronic
expansion valve
Ending conditions
Defrosting control time is no less than 135S and fulfill one of the conditions below:

Pc-max ≥ 3.0MPa.

Total defrosting control time has reached 9 minutes.

T3_min >Target value for a certain time.
Wiring
diagram
Control before Defrosting
label
INV1 Reduce frequency step
FANA
PI control
FANB
ST1 ON
Compressor operation, 2880pls
EEVA
Compressor not operation, initial 135pls, then adjusted according to the module temperature
EEVC 0pls
SV5 ON
Compressor operation, ON
SV8A
Compressor not operation, OFF
SV7 Turn ON/OFF based on the low pressure and the high pressure etc.
Normal Operation Control
EVBA
EVBB Normal Operation Control
EVBC Normal Operation Control
EEVA Normal Operation Control
Normal Operation Control
SV(n)A
Normal Operation Control
SV(n)B
Normal Operation Control
SVP
EEVA Normal Operation Control
End if Pc-Pe<0.4MPa,
Maximum 120S
Defrosting operation control
Defrosting control
One ODU unit system: 28Hz,
upper limit 88Hz
Two ODU units system: 56Hz,
upper limit 176Hz
Three ODU units system: 84Hz,
upper limit 264Hz
Initial OFF
But 10 Step or higher if the high
pressure is larger than 2.2MPa.
Compressor operation, 17pls→ +8pls per 20S based on high pressure
or discharge temperature.
Compressor not operation, 0pls.
2950pls
0pls
2950pls
0pls
ON
OFF
OFF
0pls
Defrost completion condition
judgment, maximum time is
9min
V6R VRF 50/60Hz
Control after Defrosting
Current frequency
PI control
enters PI control
Initial step then PI control
Initial step according to ambient
temperature and indoor load
Normal Operation Control
Normal Operation Control
Normal Operation Control
Normal Operation Control
Normal Operation Control
Normal Operation Control
Normal Operation Control
Normal Operation Control
90S or
Pc-Pe<0.4MPa After 30S
for 20S
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