Carrier 19XR, XRV specifications Troubleshooting Guide, Checking Pressure Transducers

TROUBLESHOOTING GUIDE

Overview — The PIC II has many features to help the op- erator and technician troubleshoot a 19XR chiller.

•The CVC/ICVC shows the chiller’s actual operating con- ditions and can be viewed while the unit is running.

•The CVC/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 CVC/ICVC default screen returns to normal operation.

•The CONTROL ALGORITHM STATUS screens (which include the CAPACITY, OVERRIDE, LL_MAINT, ISM_HIST, LOADSHED, WSMDEFME, 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.

•The control test feature facilitates the proper operation and test of temperature sensors, pressure transducers, the guide vane actuator, oil pump, water pumps, tower con- trol, 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 CVC/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 gen- erated and displayed on the CVC/ICVC default screen. A more detailed message — along with a diagnostic message — is also stored into the ALARM HISTORY table.

Checking Display Messages — The first area to check when troubleshooting the 19XR is the CVC/ICVC dis- play. If the alarm light is flashing, check the primary and sec- ondary message lines on the CVC/ICVC default screen (Fig. 14). These messages will indicate where the fault is oc- curring. These messages contain the alarm message with a specified code. This code or state appears with each alarm and alert message. The ALARM HISTORY table on the CVC/ ICVC SERVICE menu also contains an alarm message to fur- ther expand on the alarm. For a complete list of possible alarm messages, see Table 11. 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.

Checking Temperature Sensors — All temperature sensors are thermistor-type sensors. This means that the resis- tance of the sensor varies with temperature. All sensors have the same resistance characteristics. If the controls are on, deter- mine sensor temperature by measuring voltage drop; if the con- trols are powered off, determine sensor temperature by measur- ing resistance. Compare the readings to the values listed in Table 12A or 12B.

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 12A or 12B. Check the resistance of both wires to ground. This resistance should be infinite.

VOLTAGE DROP — The voltage drop across any energized sensor can be measured with a digital voltmeter while the con- trol is energized. Table 12A or 12B lists the relationship be- tween 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 con- trol is powered on.

Relieve all refrigerant pressure or drain the water before replacing the temperature sensors.

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° F (.25° C) graduations. The sensor in question should be accurate to within 2° F (1.2° C).

See Fig. 9 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 — For servicing con- venience, there are 2 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 2 terminal in the sensor terminal box is the common line. To use the sec- ond sensor, move the wire from the number 1 position to the number 3 position.

Checking Pressure Transducers

UNITS EQUIPPED WITH CVC — There are 8 pressure transducers on 19XR chillers. They determine cooler, condens- er, oil pressure, and cooler and condenser flow. The cooler and condenser transducers are also used by the PIC II to determine the refrigerant temperatures. The oil supply pressure transducer value and the oil transmission sump pressure transducer value difference is calculated by the CCM. The CVC module then displays the differential pressure. In effect, the CVC reads only one input for oil pressure for a total of 5 pressure inputs: cooler pressure, condenser pressure, oil differential pressure, cooler waterside differential pressure, and condenser waterside differ- ential pressure. See the Check Pressure Transducers section (page 75) under Scheduled Maintenance.

UNITS EQUIPPED WITH ICVC — There are 6 factory- installed pressure transducers, with inputs available for both cooler and The ICVC software will display a default reading of 26 psi during start-up and operation. An additional transducer, factory installed in the bottom of the cooler barrel, will read as EVAPORATOR SACTURATION 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 calibrate the transducers to ensure the proper refrigerant temperature/ pressure relationship. Each transducer is supplied with 5 vdc 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 supply voltage. It should be 5 vdc ±.5 v displayed in CONTROL TEST under CCM Pressure Transducers. If the supply voltage is correct, the trans- ducer should be recalibrated or replaced.

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