Trane TVR Pro CO Series Service Manual page 34

6.2 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".
Timing of oil return operation:
 When the initial cumulative operating time reaches 140 minutes and then every 8 hours.
Tables 3-6.1 and 3-6.2 show component control during oil return operation in cooling mode.
Table 3-6.1: Outdoor unit component control during oil return operation in cooling mode
Component
Inverter compressor A
Inverter compressor B
DC fan motor A
DC fan motor B
Electronic expansion valve A
Solenoid valve (Liquid injection)
Solenoid valve (oil balance)
Solenoid valve (refrigerant bypass)
Wiring diagram label
BP1
BP2
FAN1
FAN2
EXVA
SV2
SV4
SV7
Table 3-6.2: Indoor unit component control during oil return operation in cooling mode
Component
Fan
Electronic expansion valve
8-12HP 14-16HP 18-22HP
● ●
● ●
● ●
● ●
● ●
● ●
Unit state Control functions and states
Thermo on Remote controller setting
Standby Off
Thermo off Off
Thermo on Normal control
Standby 300 (steps)
Thermo off 300 (steps)
33
24-30HP Control functions and states
● ●
Fixed frequency
● ●
Controlled
● ●
discharge pressure
● ●
Position 480 (steps)
● ●
Normal control
● ●
Normal control
● ●
Normal control
● ●
according to