Capacity Override (Table 6); High Discharge Temperature Control; Oil Sump Temperature And Pump Control; Oil Cooler - Carrier 19XRV Start-Up, Operation And Maintenance Instructions Manual

If kilowatts is selected for the DEMAND LIMIT SOURCE,
the MOTOR RATED LOAD KILOWATTS must be
entered in the VFD_CONF screen.
The TEMP PULLDOWN DEG/MIN may be viewed or
modified on the TEMP_CTL screen which is accessed
from the EQUIPMENT SERVICE screen. PULLDOWN
RAMP TYPE, DEMAND LIMIT SOURCE, and AMPS
OR KW RAMP %/MIN may be viewed or modified on the
RAMP_DEM screen.

5.8 - Capacity override (Table 6)

Capacity overrides can prevent some safety shutdowns
caused by exceeding the motor amperage limit, low evapo-
rator temperature safety limit, high motor temperature
safety limit, and high condenser pressure limit. In all cases,
there are two stages of compressor capacity control
applied by guide vane operation:
1. When the value of interest crosses the First Stage Set
Point into the Override Region, the guide vanes are
prevented from opening further, and the status line on
the ICVC indicates the reason for the override. Normal
capacity control operation is restored when the value
crosses back over the First Stage Set point, leaving the
Override Region. See Table 6.
. When the value of interest is in the Override Region
and further crosses the Second Stage Set Point, the
guide vanes are closed until the value meets the
Override Termination Condition. The PIC III controls
resume normal capacity control operation after the
override termination condition has been satisfied. (In
the case of high discharge superheat, there is an
intermediate stage.)
Whenever the motor current demand limit set point
(ACTIVE DEMAND LIMIT) is reached, it activates a
capacity override, again, with a -step process. Exceeding
110% of the rated load amps for more than 30 seconds will
initiate a safety shutdown.
The high compressor lift (surge prevention) set point will
cause a capacity override as well. When the surge prevention
set point is reached, the controller normally will only
prevent the guide vanes from opening. If so equipped, the
hot gas bypass valve will open instead of holding the vanes.
The hot gas bypass will only open if the compressor is at
100% speed. See the Surge Prevention Algorithm section,
page 43.

5.9 - High discharge temperature control

If the COMP DISCHARGE TEMP increases above 71.1°C,
the guide vanes are proportionally opened to increase gas
flow through the compressor. If the LEAVING CHILLED
WATER temperature decreases .8 K below the control set
point temperature, as a result of opening the guide vanes,
the PIC III will bring the chiller into the recycle mode.

5.10 - Oil sump temperature and pump control

The oil sump temperature is regulated by the PIC III, with
the oil heater relay when the chiller is shut down.
As part of the pre-start checks executed by the controls, the
oil sump temperature (OIL SUMP TEMP) is compared to
the evaporator refrigerant temperature (EVAPORATOR
REFRIG TEMP) if the OIL SUMP TEMP is less than
65.6°C. If the difference between these  temperatures is
7.8 K or less, the start-up will be delayed until either of
these conditions is no longer true. Once this temperature
criteria is satisfied, the start-up continues.
The oil heater relay is energised whenever the chiller
compressor is off and the oil sump temperature is less than
60°C or the OIL SUMP TEMP is less than the EVAP
REFRIG TEMP plus 9.4 K. The oil heater is turned off
when the OIL SUMP TEMP is either:
• more than 66.7°C, or
• more than 61.1°C and more than the EVAP REFRIG
TEMP plus 30.6 K.
The oil heater is always off during start-up or when the
compressor is running.
The oil pump is also energised during the time the oil is
being heated (for 30 seconds at the end of every 30 minutes).
The oil pump will not operate if the EVAPORATOR
PRESSURE is less than –34.5 kPa.

5.11 - Oil cooler

The oil must be cooled when the compressor is running.
This is accomplished through a small, plate-type heat
exchanger (also called the oil cooler) located behind the oil
pump. The heat exchanger uses liquid condenser refrigerant
as the cooling liquid. Refrigerant thermostatic expansion
valves (TXVs) regulate refrigerant flow to control the oil
temperature entering the bearings. The bulbs for the
expansion valves are strapped to the oil supply line leaving
the heat exchanger, and the valves are set to maintain 43°C.
NOTE: The TXVs are not adjustable. The oil sump tempe-
rature may be lower during compressor operation.
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