CHECK SENSOR ACCURACY — Place the sensor in a
medium of a known temperature and compare that tempera-
ture to the measured reading. The thermometer used to de-
termine the temperature of the medium should be of labo-
ratory quality with 0.5° F (.25° C) graduations. The sensor
in question should be accurate to within 2° F (1.2° C).
See Fig. 7 and 8 for sensor locations. The sensors are im-
mersed directly in the refrigerant or water circuits. The wir-
ing at each sensor is easily disconnected by unlatching the
connector. These connectors allow only one-way connection
to the sensor. When installing a new sensor, apply a pipe
sealant or thread sealant to the sensor threads.
DUAL TEMPERATURE SENSORS — There are 2 sensing
elements on each of the bearing temperature sensors (her-
metic and open-drive machines) and motor temperature sen-
sors (hermetic machines only) for servicing convenience. In
case one of the dual sensors is damaged, the other one can
be used by moving a wire.
The number 1 terminal in the sensor terminal box is the
common line. To use the second sensor, move the wire from
the number 2 position to the number 3 position.
Checking Pressure Transducers — There are 3 pres-
sure transducers on hermetic machines. These determine cooler,
condenser, and oil pressure. Open-drive machines have 4 trans-
ducers. These transducers sense cooler pressure, condenser
pressure, oil supply pressure, and oil sump pressure. The oil
supply pressure and the oil transmission sump pressure dif-
ference is calculated by a differential pressure power supply
module on open-drive machines. The PSIO then reads this
differential. In effect, then, the PSIO reads 3 pressure inputs
for open-drive machines and 3 pressure inputs for hermetic
machines. The cooler and condenser transducers are used by
the PIC to determine refrigerant temperatures.
All pressure inputs can be calibrated, if necessary. It is not
usually necessary to calibrate at initial start-up. However, at
high altitude locations, calibration of the transducer will be
necessary to ensure the proper refrigerant temperature/
pressure relationship. Each transducer is supplied with 5 vdc
power from a power supply. If the power supply fails, a trans-
ducer voltage reference alarm will occur. If the transducer
reading is suspected of being faulty, check the supply volt-
age. It should be 5 vdc ± .5 v. If the supply voltage is cor-
rect, the transducer should be recalibrated or replaced.
IMPORTANT: For hermetic machines, whenever the
oil pressure or the cooler pressure transducer is cali-
brated, the other sensor should be calibrated to pre-
vent problems with oil differential pressure readings.
To calibrate oil pressure differential on open-drive ma-
chines, refer to Oil Pressure Differential Calibration at the
end of this section.
Calibration can be checked by comparing the pressure read-
ings from the transducer against an accurate refrigeration gage.
These readings are all viewed or calibrated from the
Status01 table on the LID. The transducer can be checked
and calibrated at 2 pressure points. These calibration points
are 0 psig (0 kPa) and between 240 and 260 psig (1655 to
1793 kPa). To calibrate these transducers:
1. Shut down the compressor.
2. Disconnect the transducer in question from its Schrader
fitting.
NOTE: If the cooler or condenser vessels are at 0 psig
(0 kPa) or are open to atmospheric pressure, the trans-
ducers can be calibrated for zero without removing the
transducer from the vessel.
3. Access the Status01 table, and view the particular trans-
ducer reading; it should read 0 psi (0 kPa). If the reading
is not 0 psi (0 kPa), but within ± 5 psi (35 kPa), the
value may be zeroed by pressing the SELECT
softkey
while the highlight bar is located on the transducer, and
then by pressing the ENTER
. The value will now go
to zero.
If the transducer value is not within the calibration range,
the transducer will return to the original reading. If the
LID pressure value 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 trans-
ducer by the supply voltage signal, measured at the PSIO
terminals J7-J34 and J7-J35. For example, the condenser
transducer voltage input is measured at PSIO terminals
J7-1 and J7-2. The voltage ratio must be between
0.80 vdc and 0.11 vdc for the software to allow calibra-
tion. Pressurize the transducer until the ratio is within range.
Then attempt calibration again.
4. A high pressure point can also be calibrated between 240
and 260 psig (1655 and 1793 kPa) by attaching a regu-
lated 250 psig (1724 kPa) pressure (usually from a ni-
trogen cylinder). The high pressure point can be calibrated
by accessing the transducer on the Status01 screen,
highlighting the transducer, pressing the SELECT
soft-
key, and then increasing or decreasing the value to the
exact pressure on the refrigerant gage. Press ENTER
to finish. High altitude locations must compensate the pres-
sure so that the temperature/pressure relationship is
correct.
If the transducer reading returns to the previous value and
the pressure is within the allowed range, check the volt-
age ratio of the transducer. Refer to Step 3 above. The
voltage ratio for this high pressure calibration must be
between 0.585 and 0.634 vdc to allow calibration. Change
the pressure at the transducer until the ratio is within the
acceptable range. Then attempt calibrate to the new pres-
sure input.
The PIC will not allow calibration if the transducer is too
far out of calibration. A new transducer must be installed
and re-calibrated.
OIL DIFFERENTIAL PRESSURE/POWER SUPPLY MOD-
ULE CALIBRATION — (See Fig. 48.) The oil reservoir in
the 17EX machine is not common to cooler pressure. There-
fore, a comparison of pump output to cooler pressure could
not be used to provide differential oil pressure information.
A different method has been developed.
Oil transmission sump pressure and oil supply pressure
are fed to a comparator circuit on a 5V power supply board.
The output of this circuit, which represents differential oil
pressure, is fed to the PSIO. The oil differential pressure is
calibrated to zero PSIO (0 kPad) by selecting the oil pres-
sure input on the Service1 screen. Then, with the oil pump
turned OFF and the transducers CONNECTED, press EN-
TER to zero the point. No high end calibration is needed or
possible.
84
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