TROUBLESHOOTING GUIDE
Overview Ð The PIC has many features to aid the operator and the technician in troubleshooting a 19XL chiller.
·By using the LID display, the chiller actual operating con- ditions can be viewed while the unit is running.
·When an alarm occurs, the default LID screen will freeze at the time of alarm. The freeze enables the operator to view the chiller conditions at the time of alarm. The Status tables will still show the current information. Once all alarms have been cleared, the default LID screens will return to normal operation.
·The Control Algorithm Status tables will display various screens of information in order to diagnose problems with chilled water temperature control, chilled water temper- ature control overrides, hot gas bypass, surge algorithm status, and time schedule operation.
·The Control Test feature allows proper operation and test- ing 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 compressor and turn on water pumps for pumpout operation. The display will show the required temperatures and pressures during these operations.
·Other Service menu tables can access con®gured items, such as chilled water resets, override set points, etc.
·If an operating fault is detected, an alarm message is gen- erated and displayed on the LID default screen. A more detailed message Ð along with a diagnostic message Ð also is stored into the Alarm History table.
Checking the Display Messages Ð The ®rst area to check when troubleshooting the 19XL is the LID display. If the alarm light is ¯ashing, check the primary and second- ary message lines on the LID default screen (Fig. 13). These messages will indicate where the fault is occurring. The Alarm History table on the LID Service menu will also carry an alarm message to further expand on this alarm. For a com- plete listing of messages, see Table 9. If the alarm light starts to ¯ash while accessing a menu screen, depress
EXIT to return to the Default screen to read the failure
message. The compressor will not run with an alarm con- dition existing, unless the alarm type is an unauthorized start or a failure to shut down.
Checking Temperature Sensors Ð All tempera- ture sensors are of the thermistor type. This means that the resistance of the sensor varies with temperature. All sensors have the same resistance characteristics. Determine sensor temperature by measuring voltage drop if the controls are powered, or resistance if the controls are powered off. Com- pare the readings to the values listed in Tables 10A or 10B.
RESISTANCE CHECK Ð Turn off the control power and disconnect the terminal plug of the sensor in question from the module. Measure sensor resistance between recep- tacles designated by the wiring diagram with a digital ohm- meter. The resistance and corresponding temperature is listed in Tables 10A or 10B. Check the resistance of both wires to ground. This resistance should be in®nite.
VOLTAGE DROP Ð Using a digital voltmeter, the voltage drop across any energized sensor can be measured while the control is energized. Tables 10A or 10B lists the relation- ship between temperature and sensor voltage drop (volts dc measured across the energized 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 vdc if the control is powered.
Relieve all refrigerant pressure or drain the water prior to replacing the temperature sensors.
CHECK SENSOR ACCURACY Ð Place the sensor in a medium of a known temperature and compare that temper- ature to the measured reading. The thermometer used to determine the temperature of the medium should be of lab- oratory quality with 0.5° F (.25° C) graduations. The sensor in question should be accurate to within 2° F (1.2° C).
See Fig. 8 for sensor locations. 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.
DUAL TEMPERATURE SENSORS Ð There are 2 sensors each on the bearing and motor temperature sensors for servicing convenience. In case one of the dual sensors is damaged, the other one can be used by moving a wire.
The number 2 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.
Checking Pressure Transducers Ð There are 3 pressure transducers on the 19XL. These determine cooler, condenser, and oil pressure. The cooler and condenser trans- ducers also are used by the PIC to determine the refrigerant temperatures. All 3 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 transducer voltage reference alarm will occur. If the trans- ducer reading is suspected of being faulty, check the supply voltage. It should be 5 vdc ± .5 v. If the supply voltage is correct, the transducer should be recalibrated or replaced.
IMPORTANT: Whenever the oil pressure or the cooler pressure transducer is calibrated, the other sensor should be calibrated to prevent problems with oil differential pressure readings.
Calibration can be checked by comparing the pressure readings from the transducer against an accurate refrig- eration 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 ®tting.
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.
