Checking Pressure Transducers; High Altitude Locations; Quick Test; Pumpdown/Lockout - Carrier AquaEdge 19XR Start-Up, Operation And Maintenance Instructions Manual

Checking Pressure Transducers

There are 4 typically factory-installed pressure transducers
measuring refrigerant and oil pressure and, if equipped, a fifth
pressure transducer measuring economizer pressure.
These transducers can be calibrated if necessary. It is necessary
to calibrate at initial start-up, particularly at high altitude loca-
tions, to ensure the proper refrigerant temperature/pressure re-
lationship. Each transducer is supplied with 5 vdc power. If the
power supply fails, a transducer voltage reference alarm oc-
curs. If the transducer reading is suspected of being faulty,
check the TRANSDUCER VOLTAGE REF supply voltage. It
should be 5 vdc ± 0.5 v as displayed in MAINTENANCE
MENU  MAINTENANCE OTHERS, where all the trans-
ducer voltages are shown. If the TRANSDUCER VOLTAGE
REF supply voltage is correct, the transducer should be recali-
brated or replaced.
Also check that inputs have not been grounded.
PRESSURE TRANSDUCER REPLACEMENT
Since the transducers are mounted on Schrader-type fittings, there
is no need to remove refrigerant from the vessel when replacing
the transducers. Disconnect the transducer wiring. Do not pull on
the transducer wires. Unscrew the transducer from the Schrader
fitting. When installing a new transducer, do not use pipe sealer
(which can plug the sensor). Put the plug connector back on the
sensor and snap into place. Check for refrigerant leaks.
WARNING
Be sure to use a back-up wrench on the Schrader fitting
whenever removing a transducer, since the Schrader fitting
may back out with the transducer, causing a large leak and
possible injury to personnel.
COOLER AND CONDENSER PRESSURE TRANSDUCER
CALIBRATION
Calibration can be checked by comparing the pressure readings
from the transducer to an accurate refrigeration gage reading.
These readings can be viewed or calibrated from the HMI
screen. The transducer can be checked and calibrated at 2 pres-
sure points. These calibration points are 0 psig (0 kPa) and be-
tween 25 and 250 psig (173 and 1724 kPa). Wiring is shown in
Fig. 51. Installation of pressure transducers into water nozzles
using flushable dirt leg trap is suggested; see Fig. 52. Connect
pressure transducer to Schrader connection. To enable this op-
tion, IOB4 must be activated and the Option must be selected in
the Option Configuration menu. To calibrate these transducers:
1. Shut down the compressor, cooler, and condenser pumps.
NOTE: There should be no flow through the heat exchangers.
2. Disconnect the transducer in question from its Schrader
fitting for cooler or condenser transducer calibration. For
oil pressure or flow device calibration, leave the trans-
ducer in place.
NOTE: If the cooler or condenser vessels are at 0 psig
(0 kPa) or are open to atmospheric pressure, the transduc-
ers can be calibrated for zero without removing the trans-
ducer from the vessel.
3. Access the PRESSURE or HYDRAULIC STATUS screen
and view the particular transducer reading. To calibrate oil
pressure or waterside flow device, view the particular
reading. It should read 0 psig (0 kPa). If the reading is not
0 psig (0 kPa), but within ± 5 psig (35 kPa), the value may
be set to zero from the Maintenance Menu while the
appropriate transducer parameter is highlighted. The value
will now go to zero.
If the transducer value is not within the calibration range,
the transducer returns to the original reading. If the pressure
is within the allowed range (noted above), check the voltage
ratio of the transducer. To obtain the voltage ratio, divide the
voltage (dc) input from the transducer by the supply voltage
signal or measure across the positive (+ red) and negative (–
black) leads of the transducer. The input to reference volt-
age ratio must be between 0.80 and 0.11 for the software to
allow calibration. Rotate the waterside flow pressure device
from the inlet nozzle to the outlet nozzle and repeat this
step. If rotating the waterside flow device does not allow
calibration, pressurize the transducer until the ratio is within
range. Then attempt calibration again.
4. Pressures can be calibrated between 100 and 250 psig
(689.5 and 1723.7 kPa) by attaching a regulated 250 psig
(1724 kPa) pressure (usually from a nitrogen cylinder).
For calibration, access the Pressure Sensor Calibration
Menu from the Maintenance Menu and calibrate the
appropriate sensor.
The PIC 6 control system does not allow calibration if the trans-
ducer is too far out of calibration. In this case, a new transducer
must be installed and re-calibrated. If calibration problems are en-
countered on the OIL PRESSURE DELTA P channel, sometimes
swapping the compressor oil discharge pressure transducer and
the oil sump pressure transducer will offset an adverse transducer
tolerance stack up and allow the calibration to proceed.
HYDRAULIC STATUS
The HYDRAULIC STATUS screen (access from the Main
Menu) provides a convenient way to detect if any of the cooler/
condenser pressure switches (if installed) are in need of cali-
bration. With no flow and no added resistors the water delta
should read zero psig (0 kPa). If it does not, the value may be
set to zero using PRESSURE SENSOR CALIB located in the
Maintenance Menu.

High Altitude Locations

Because the chiller is initially calibrated at sea level, it is necessary
to recalibrate the pressure transducers if the chiller has been
moved to a high altitude location. See the calibration procedure in
the 19XR with PIC 6 Controls Operation and Troubleshooting
guide. Note that Atmospheric Pressure can be adjusted in the Ser-
vice Parameters Menu (located in the Configuration Menu).

Quick Test

The Quick Test feature is located in the Main Menu. Use this
feature to test guide vanes, test chiller status, test the status of
various actuators, view water temperature deltas, and test oil
pump and oil heater relays, as well as control inlet guide vane,
hot gas bypass, economizer damper, alarms, condenser, and
chilled water pumps. The tests can help to determine whether a
switch is defective or a pump relay is not operating, as well as
other useful troubleshooting issues. During pumpdown opera-
tions, the pumps are energized to prevent freeze-up and the ves-
sel pressures and temperatures are displayed. Note that prior to
Quick Test, components with feedback needs to be calibrated in
Quick Calibration.

Pumpdown/Lockout

The Pumpdown/Lockout feature, available from the Mainte-
nance Menu, prevents compressor start-up when there is no re-
frigerant in the chiller or if the vessels are isolated. The Termi-
nate Lockout feature ends the Pumpdown/Lockout after the
pumpdown procedure is reversed and refrigerant is added.

Physical Data

Tables 15-45 and Fig. 53-69 provide additional information on
component weights, compressor fits and clearances, physical
and electrical data, and wiring schematics for the operator's
convenience during troubleshooting.
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