Motor Cooling - Daikin WCT Series Operating & Maintenance Manual

run (prelube) to provide oil to the bearings. It also runs after compressor shutdown to lubricate the
bearings during coast down (postlube).
During idle periods, the oil in the sump tends to absorb as much refrigerant as it can hold, depending
upon the oil temperature and sump pressure. Lower oil temperature will increase of amount of
refrigerant absorbed that can cause violent foaming during compressor start-up, as the system pressure is
lowered. Refrigerant bubbles out of the oil during that time and the subsequent foaming can affect the
oil pump operation and system oil differential pressure.
The oil is pumped to the internal oil filter in the compressor casting and then to the external refrigerant-
cooled oil cooler through a factory pre-set pressure regulator valve. It maintains above 22 psi as
minimum, and around 50psi(50Hz) / 36psi(60Hz) as normal oil differential pressure (the difference
between the oil sump and oil supply pressure to gear/bearings).
A plate-type oil cooler maintains the proper oil temperature under normal operating conditions. A TXV
valve maintains less than max 140°F (60°C) oil supply temperature by regulating the flow of subcooled
refrigerant liquid from the condenser to the cooler.
A typical flow diagram is shown in Figure 4.
Manual isolation stop valves in the oil line and drain connections on the lubricant sump are provided for
ease of servicing.

Motor Cooling

The high pressure subcooled liquid refrigerant flows through a filter-drier to the low pressure area in the
motor housing, for motor cooling purpose. The refrigerant gas returns to the evaporator after cooling
the motor.
The flow is motivated by the pressure difference between the condenser and the evaporator.
OMM WCT Centrifugal Chillers D-EOMWC01302-16EN - 10/84