Operating Principles Mechanical
RTHD-SVX02H-EN 79
ate diagnostics and would enforce a compressor “cool
down” period.
To ensure proper lubrication and minimize refrigerant
condensation in the oil sump, heaters are mounted on
the bottom of the oil sump. An auxilliary contact of the
compressor starter, energizes these heaters during the
compressor off cycle to maintain a proper elevation of
the oil temperature. The heater element is continuously
energized while the compressor is off and does not cycle
on temperature.
Oil Filter
All Series R chillers are equipped with replaceable-ele-
ment oil filters. Each removes any impurities that could
foul the compressor internal oil supply galleries. This
also prevents excessive wear of compressor rotor and
bearing surfaces and promotes long bearing life. Refer
to the Section 9 for recommended filter element replace-
ment intervals.
Compressor Bearing Oil Supply
Oil is injected into the rotor housing where it is routed
to the bearing groups located in the motor and bearing
housing sections. Each bearing housing is vented to
compressor suction so oil leaving the bearings returns
through the compressor rotors to the oil separator.
Compressor Rotor Oil Supply
Oil flowing through this circuit enters the bottom of the
compressor rotor housing. From there it is injected along
the rotors to seal clearance spaces around the rotors and
lubricate the contact line between the male and female
rotors.
Lubricant Recovery
Despite the high efficiency of the oil separators, a small
percentage of oil will get past them, move through the
condenser, and eventually end up in the evaporator. This
oil must be recovered and returned to the oil sump. The
function of active oil return is accomplished by a pres-
sure-actuated pump referred to as the “gas pump.”
The gas pump, mounted just beneath the evaporator, is
a cylinder with four ports controlled by two solenoids.
The pump serves to return accumulating oil in the evap-
orator to the compressor at regular time intervals. As
the refrigerant- oil mixture enters the gas pump from the
bottom of the evaporator, a fill solenoid opens to allow
refrigerant vapor to be vented into the top of the evapo-
rator, and is then closed. A second solenoid then opens
to allow refrigerant at condenser pressure to enter the
gas pump. Simultaneously, a check valve prevents re-
verse flow back into the evaporator. A liquid refrigerant
and oil mixture is displaced from the gas pump cylinder
and is directed through a filter to the compressor. The oil
then combines with oil injected into the compressor and
returns to the oil sump via the oil separators.
Oil Cooler
The oil cooler is a brazed plate heat exchanger located
near the oil filter. It is designed to transfer approximate-
ly one ton of heat from the oil to the suction side of the
system. Subcooled liquid is the cooling source.
The oil cooler is required on units running at high con-
densing or low suction temperatures. The high discharge
temperatures in these applications increase oil tempera-
tures above the recommended limits for adequate lubri-
cation and reduce the viscosity of the oil.
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