Checking Pressure Transducers - Carrier 19XRV Start-Up, Operation And Maintenance Instructions Manual

7.3.4 - Dual-temperature sensors
For servicing convenience, there are  sensors each on the
bearing and motor temperature sensors. If one of the sensors
is damaged, the other can be used by simply moving a wire.
The number  terminal in the sensor terminal box is the
common line. To use the second sensor, move the wire
from the number 1 position to the number 3 position.

7.4 - Checking pressure transducers

There are 6 factory-installed pressure transducers, with
inputs available for optional cooler and condenser water-
side differential pressure transducers. The ICVC software
will display a default reading of 179 kPa during start-up and
operation. An additional transducer, factory installed in
the bottom of the cooler barrel, will read as EVAPORATOR
SATURATION TEMP on the HEAT_EX DISPLAY screen.
This provides additional protection against a loss of water
flow condition.
These pressure transducers can be calibrated if necessary.
It is not usually necessary to calibrate at initial start-up.
However, at high altitude locations, it is necessary to cali-
brate the transducers to ensure the proper refrigerant
temperature/pressure relationship. Each transducer is
supplied with 5 V d.c. power from the CCM. If the power
supply fails, a transducer voltage reference alarm occurs. If
the transducer reading is suspected of being faulty, check
the TRANSDUCER VOLTAGE REF supply voltage. It
should be 5 V d.c. ± 0.5 V displayed in CONTROL TEST
under CCM PRESSURE TRANSDUCERS. If the TRANS-
DUCER VOLTAGE REF is correct, the transducer should
be recalibrated or replaced.
Also check that inputs on CCM J5-1 through J5-6 have not
been grounded and are not receiving anything other than a
4 to 0 mA signal.
7.4.1 - Cooler/condenser pressure transducer and optional
water-side flow device 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 HEAT_EX screen on the ICVC. The transducer
can be checked and calibrated at  pressure points. These
calibration points are 0 kPa and between173 and 174 kPa.
To calibrate these transducers:
1. Shut down the compressor, cooler, and condenser
pumps.
note: There should be no flow through the heat
exchangers.
. Disconnect the transducer in question from its Schrader
fitting for cooler or condenser transducer calibration.
For oil pressure or flow device calibration, leave the
transducer in place.
note: If the cooler or condenser vessels are at 0 kPa
or are open to atmospheric pressure, the transducers
can be calibrated for zero without removing the
transducer from the vessel.
3. Access the HEAT_EX screen and view the particular
transducer reading (the EVAPORATOR PRESSURE
or CONDENSER PRESSURE parameter on the
HEAT_EX screen). To calibrate oil pressure or liquid-
side flow device, view the particular reading (CHILLED
WATER DELTA P and CONDENSER WATER
DELTA P on the HEAT_EX screen, and OIL PUMP
DELTA P on the COMPRESS screen). It should read
0 kPa. If the reading is not 0 kPa, but within ± 35 kPa,
the value may be set to zero by pressing the SeLeCt
softkey while the appropriate transducer parameter is
highlighted on the ICVC screen. Then press the enteR
softkey. The value will now go to zero. No high end
calibration is necessary for OIL PRESSURE DELTA P
or flow devices.
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 (d.c.) input from
the transducer by the TRANSDUCER VOLTAGE
REF supply voltage signal (displayed in CONTROL
TEST menu in the PRESSURE TRANSDUCERS
screen) or measure across the positive (+ red) and
negative (– black) leads of the transducer. For example,
the condenser transducer voltage reference is measured
at CCM terminals J-4 and J-6, the condenser trans-
ducer voltage input. The input to reference voltage
ratio must be between 0.80 and 0.11 for the software to
allow calibration. Pressurise the transducer until the
ratio is within range. Then attempt calibration again.
4. A high pressure point can also be calibrated between
17.4 and 173.7 kPa by attaching a regulated 174 kPa
pressure (usually from a nitrogen cylinder). The high
pressure point can be calibrated by accessing the
appropriate transducer parameter on the HEAT_EX
screen, highlighting the parameter, pressing the
SeLeCt softkey, and then using the InCReASe or
DeCReASe softkeys to adjust the value to the exact
pressure on the refrigerant gauge. Press the enteR
softkey to finish the calibration. Pressures at high
altitude locations must be compensated for, so the
chiller temperature/pressure relationship is correct.
The PIC III does not allow calibration if the transducer is
too far out of calibration. In this case, a new transducer
must be installed and re-calibrated. If calibration problems
are encountered 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.
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