Special Control; Oil Return Operation; Cooling Only/Main Cooling Oil Return Control; Timing Of Oil Return Operation - Midea VRF Series Service Manual

7 Special Control

7.1 Oil Return Operation

In order to prevent compressors from running out of oil, the oil return operation is conducted to recover oil that has flowed
out of the compressor(s) and into the piping system. This operation is performed for all units including units that are in
standby.
When the outdoor unit is running in oil return, the digital display on outdoor main PCB will display "d0".

Cooling Only/Main Cooling Oil Return Control

Timing of oil return operation:


Calculated oil discharge has reached to specified level. The higher the compressor frequency step is, the more oil
discharge.

Initial cumulative compressor operating time reaches 2 hours.

Cumulative compressor operating time reaches 8 hours.
Tables 3-7.1 and Tables 3-7.2 show component control during oil return operation in cooling only/main cooling mode.
Table 3-7.1: Outdoor unit and MS component control during oil return operation in cooling only/main cooling mode
Component
Inverter
compressor
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
Wiring diagram
STEP1
label
PI control, the minimum
step is as follows:
8-10HP 28Hz
INV1
12-22HP 61Hz
24-34HP 105HZ
36-60HP 165Hz
FANA
PI control(Cooling Only)
FANB
ST1 ON
Compressor operation, 2880pls
EEVA
Compressor not operation, initial 135pls, then adjusted according to the module temperature
EEVC 0pls
SV5 ON
SV8A ON
SV7 OFF
2950pls
EVBA
EVBB 0pls
EVBC 2950pls
EEVA 0pls
ON
SV(n)A
OFF
SV(n)B
OFF
SVP
EEVA 0pls
End if startup time arrives
150S.
Cooling oil return control
STEP2
8-10HP 28Hz
12-22HP 61Hz
24-34HP 105HZ
36-60HP 165Hz
Compressor operation, 17pls→ +8pls per 20S based on high
pressure or discharge temperature.
Compressor not operation, 0pls.
End if startup time arrives 6
min or the compressor
discharge volume ≥ Target
value for 4min.
V6R VRF 50/60Hz
STEP3
Minimum step(All outdoor unit
compressors are running).
Back to the state before oil return
Refer to normal operation control
Turn ON/OFF based on the low
pressure and the high pressure etc.
After 30S.
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