Trane R Series Installation Operation & Maintenance page 88

Operating Principles
As the oil leaves the separator, it passes through the oil cooler. It then goes
through the service valve and filter. At this point it travels through the master
oil valve. Then it splits to feed the male load/unload solenoid valves and to
provide oil injection and bearing lubrication.
If the compressor stops for any reason, the master oil valve closes, isolating
the oil charge in the separator and oil cooler during "off' periods. The master
oil valve is a pressure activated valve. Discharge pressure off the rotors, that
is developed when the compressor is on, causes the valve to open.
Oil Separator
The oil separator consists of a vertical tube, joined at the top by the refrig-
erant discharge line from the compressor. This causes the refrigerant to swirl
in the tube and throws the oil to the outside, where it collects on the walls
and flows to the bottom. The compressed refrigerant vapor, stripped of oil
droplets, exits out the top of the oil separator and is discharged into the
condenser.
Compressor Bearing Oil Supply
Oil is injected into the bearing housings located at each end of both the male
and female rotors. Each bearing housing is vented to compressor suction, so
that oil leaving the bearings returns through the compressor rotors to the oil
separator.
Compressor Rotor Oil Supply
Oil flows through this circuit directly from the master oil filter, through the
master oil valve to the top of the compressor rotor housing. There it is
injected along the top of the rotors to seal clearance spaces between the
rotors and the compressor housing and to lubricate the rotors.
Female Unloader Valve
The position of the female unloader valve determines compressor capacity.
Its position is dependent on whether the backside of the female unloader
valve is exposed to the compressor discharge or suction pressure. See
Figure 37.
The female unloader valve receive a constant signal from the UCM, based on
system cooling requirements. To load the compressor, the female unloader
valve is energized and discharge pressure is passed through the normally-
closed port and into the cylinder. This pushed the female unloader valve
closed.
To unload the compressor, the female unloader valve solenoid is de-energized
and the discharge pressure is relieved to the suction of the compressor. The
female unloader valve retracts into the cylinder and the compressor is
unloaded.
Just prior to a normal compressor shutdown, the male unload valve solenoid
is energized and the slide valve moves to the fully-unloaded position, so the
unit always starts fully unloaded.
Oil Filter
Each compressor is equipped with a replaceable element oil filter. The filter
removes any impurities that could foul the solenoid valve orifices and
compressor internal oil supply galleries. This also prevents excessive wear of
compressor rotor and bearing surfaces. Refer to the maintenance portion of
this manual for recommended filter element replacement intervals.
RTCA Condenser Fan Staging
The fans on the RTCA 70-125 Ton units are staged by logic in the UCM of the
RTUA. The UCM takes several different pressures and temperatures into
account, to determine when fans should be added or subtracted. Input from
88 RLC-SVX07A-EN