Vfd Cooling Cycle; Lubrication Cycle; Summary; Details - Carrier AquaEdge 19XRV series Operation, Maintenance And Installation Manual

VFD COOLING CYCLE

The unit-mounted variable frequency drive (VFD) is cooled
in a manner similar to the motor and lubricating oil cooling
cycle (Fig. 6 and 7).
If equipped with a unit-mounted VFD, the refrigerant line
that feeds the motor cooling and oil cooler also feeds the heat
exchanger on the unit-mounted VFD. Refrigerant is metered
through an orifice. The refrigerant leaving the heat exchanger
returns to the cooler.

LUBRICATION CYCLE

The oil pump, oil filter, and oil cooler make
Summary —
up a package located partially in the transmission casing of the
compressor-motor assembly. The oil is pumped into a filter
assembly to remove foreign particles and is then forced into an
oil cooler heat exchanger where the oil is cooled to proper
operational temperatures. After the oil cooler, part of the flow
is directed to the gears and the high speed shaft bearings; the
remaining flow is directed to the motor shaft bearings. Oil
drains into the transmission oil sump to complete the cycle
(Fig. 6 and 7).
Oil is charged into the lubrication system through
Details —
a hand valve. Two sight glasses in the oil reservoir permit oil
level observation. Normal oil level is between the middle of the
upper sight glass and the top of the lower sight glass when the
compressor is shut down. The oil level should be visible in at
least one of the 2 sight glasses during operation. Oil sump
temperature is displayed on the ICVC (International Chiller
Visual Controller) default screen. During compressor opera-
tion, the oil sump temperature ranges between 125 and 150 F
(52 and 66 C).
The oil pump suction is fed from the oil reservoir. An oil
pressure relief valve maintains 18 to 30 psid (124 to 207 kPad)
differential pressure in the system at the pump discharge. The
normal oil pressure on compressors equipped with rolling
element bearings is between 18 and 40 psid (124 and
276 kPad). This differential pressure can be read directly from
the ICVC default screen. The oil pump discharges oil to the oil
a19-1965
REAR MOTOR
BEARING
MOTOR
COOLING LINE
OIL
FILTER
FLOW
TXV BULB PRESSURE ISOLATION
TRANSDUCER VALVES
OIL
COOLER
Fig. 6 — Single-Stage Lubrication System
filter assembly. This filter can be closed to permit removal of
the filter without draining the entire oil system (see Mainte-
nance sections, pages 87 to 93 for details). The oil is then piped
to the oil cooler heat exchanger. The oil cooler uses refrigerant
from the condenser as the coolant. The refrigerant cools the oil
to a temperature between 120 and 140 F (49 and 60 C).
As the oil leaves the oil cooler, it passes the oil pressure
transducer and the thermal bulb for the refrigerant expansion
valve on the oil cooler. The oil is then divided. Part of the oil
flows to the thrust bearing, forward pinion bearing, and gear
spray. The rest of the oil lubricates the motor shaft bearings and
the rear pinion bearing. The oil temperature is measured in the
bearing housing as it leaves the thrust and forward journal
bearings. The outer bearing race temperature is measured on
compressors with rolling element bearings. The oil then drains
into the oil reservoir at the base of the compressor. The PIC III
(Product Integrated Control III) measures the temperature of
the oil in the sump and maintains the temperature during shut-
down (see Oil Sump Temperature and Pump Control section,
page 50). This temperature is read on the ICVC default screen.
During chiller start-up, the PIC III energizes the oil pump
and provides 45 seconds of pre-lubrication to the bearings after
pressure is verified before starting the compressor. During
shutdown, the oil pump will run for 60 seconds to
post-lubricate after the compressor shuts down. The oil pump
can also be energized for testing purposes during a Control
Test.
Ramp loading can be adjusted to slow the rate of guide vane
opening to minimize oil foaming at start-up. If the guide vanes
open quickly, the sudden drop in suction pressure can cause
any refrigerant in the oil to flash. The resulting oil foam cannot
be pumped efficiently; therefore, oil pressure falls off and lu-
brication is poor. If oil pressure falls below 15 psid (103 kPad)
differential, the PIC III will shut down the compressor.
If the controls are subject to a power failure that lasts more
than 3 hours, the oil pump will be energized periodically when
the power is restored. This helps to eliminate refrigerant that
has migrated to the oil sump during the power failure. The
controls energize the pump for 30 seconds every 30 minutes
until the chiller is started.
FWD MOTOR
BEARING
LABYRINTH
GAS LINE
OIL
PUMP
OIL
HEATER
OIL PUMP
EDUCTOR FILTER
MOTOR
SIGHT
GLASS
11
OIL SUPPLY TO
FORWARD HIGH
SPEED BEARING
SIGHT
GLASS
ISOLATION
VALVE
FILTER
STRAINER
ISOLATION
VALVE
OIL SKIMMER
LINE