54
7 - TROUBLESHOOTING GUIDE (Tables 9-12)
7.1 - Overview
The PIC III has many features to help the operator and
technician troubleshoot a 19XRV chiller.
•
The ICVC shows the chiller’s actual operating condi-
tions and can be viewed while the unit is running.
•
The ICVC default screen freezes when an alarm occurs.
The freeze enables the operator to view the chiller
conditions at the time of alarm. The STATUS screens
continue to show current information. Once all alarms
have been cleared (by correcting the problems and
pressing the
ReSet
softkey), the ICVC default screen
returns to normal operation.
•
The CONTROL ALGORITHM STATUS screens
(which include the CAPACITY, OVERRIDE, LL_
MAINT, VFD_HIST, LOADSHED, CUR_ALARM,
WSM_DEFME, and OCCDEFCM screens) display
information that helps to diagnose problems with chilled
water temperature control, chilled water temperature
control overrides, hot gas bypass, surge algorithm status,
and time schedule operation. See Table 9.
•
The control test feature facilitates the proper operation
and test of temperature sensors, pressure transducers,
the guide vane actuator, oil pump, water pumps, tower
control, and other on/off outputs while the compressor
is stopped. It also has the ability to lock off the com-
pressor and turn on water pumps for pumpout opera-
tion. The ICVC shows the temperatures and pressures
required during these operations.
•
From other SERVICE tables, the operator/technician
can access configured items, such as chilled water
resets, override set points, etc.
•
If an operating fault is detected, an alarm message is
generated and displayed on the ICVC default screen.
A more detailed message - along with a diagnostic
message - is also stored into the ALARM HISTORY
and ALERT HISTORY tables.
•
Review the ALERT HISTORY table to view other
less critical events and abnormal conditions which
may have occurred. Compare timing of relevant alerts
and alarms.
7.2 - Checking display messages
The first area to check when troubleshooting the 19XRV is
the ICVC display. If the alarm light is flashing, check the
primary and secondary message lines on the ICVC default
screen (Fig. 3). These messages will indicate where the fault
is occurring. These messages contain the alarm message with
a specified code. For a complete list of possible alarm and
alert messages, see Table 10. This code or state appears
with each alarm and alert message. The ALARM and
ALERT HISTORY tables on the ICVC SERVICE menu
also contains a message to further expand on the fault
description. For a complete list of VFD Fault Code Descrip-
tions and corrective actions, see Table 11.
note:
The date format in these tables is MM/DD/YY.
If the alarm light starts to flash while accessing a menu
screen, press the
eXIt
softkey to return to the default screen
to read the alarm message. The STATUS screen can also
be accessed to determine where an alarm exists.
A “C” to the right of a parameter’s value means that there
is a communications fault on that channel.
7.3 - Checking temperature sensors
All temperature sensors are thermistor-type sensors. This
means that the resistance of the sensor varies with tempera-
ture. All sensors have the same resistance characteristics. If
the controls are on, determine sensor temperature by mea-
suring voltage drop; if the controls are powered off, deter-
mine sensor temperature by measuring resistance. Compare
the readings to the values listed in Table 1.
7.3.1 - Resistance check
Turn off the control power and, from the module, disconnect
the terminal plug of the sensor in question. With a digital
ohmmeter, measure sensor resistance between receptacles
as designated by the wiring diagram. The resistance and
corresponding temperature are listed in Table 1. Check
the resistance of both wires to ground. This resistance
should be infinite.
7.3.2 - Voltage drop
The voltage drop across any energised sensor can be mea-
sured with a digital voltmeter while the control is energised.
Table 1 lists the relationship between temperature and
sensor voltage drop (volts dc measured across the energised
sensor). Exercise care when measuring voltage to prevent
damage to the sensor leads, connector plugs, and modules.
Sensors should also be checked at the sensor plugs. Check
the sensor wire at the sensor for 5 V d.c. if the control is
powered on.
CAUTION: Relieve all refrigerant pressure or drain the
water before replacing temperature sensors or thermowells
threaded into the refrigerant pressure boundary. Failure
to do so could result in personal injury and equipment
damage.
7.3.3 - Check sensor accuracy
Place the sensor in a medium of known temperature and
compare that temperature to the measured reading. The
thermometer used to determine the temperature of the
medium should be of laboratory quality with 0.5 K
graduations. The sensor in question should be accurate to
within 1. K.
The sensors are immersed directly in the refrigerant or
water circuits. The wiring 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.