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
Cooling oil return control
PI control, the minimum
step is as follows:
8-10HP 28Hz
12-22HP 61Hz
24-34HP 105HZ
36-60HP 165Hz
8-10HP 28Hz
12-22HP 61Hz
24-34HP 105HZ
36-60HP 165Hz
Minimum step(All outdoor unit
compressors are running).
Back to the state before oil return
Electronic
expansion valve
Compressor operation, 2880pls
Compressor not operation, initial 135pls, then adjusted according to the module temperature
Compressor operation, 17pls→ +8pls per 20S based on high
pressure or discharge temperature.
Compressor not operation, 0pls.
Refer to normal operation control
Turn ON/OFF based on the low
pressure and the high pressure etc.
Electronic
expansion valve
Electronic
expansion valve
End if startup time arrives
150S.
End if startup time arrives 6
min or the compressor
discharge volume
≥
Target
value for 4min.
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