Carrier 19XR Spécifications télécharger pdf (Page 76)

TROUBLESHOOTING GUIDE

Overview —

The PIC II has many features to help the op-

erator and technician troubleshoot a 19XR chiller.

• The CVC shows the chiller’s actual operating conditions

and can be viewed while the unit is running.

• The CVC default screen freezes when an alarm occurs.

The freeze enables the operator to view the chiller condi-

tions 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

softkey), the CVC default screen returns to nor-

mal 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 tempera-

ture control, chilled water temperature control overrides,

hot gas bypass, surge algorithm status, and time sched-

ule 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 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 CVC 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 display. If

the alarm light is flashing, check the primary and secondary

message lines on the CVC default screen (Fig. 14). These mes-

sages will indicate where the fault is occurring. These messag-

es 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 SERVICE menu also

contains an alarm message to further 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 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 tempera-

ture sensors are thermistor-type sensors. This means that the re-

sistance 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.

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 —

There are 8

pressure transducers on 19XR chillers. They determine cooler,

condenser, 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 trans-

ducer 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 pres-

sure inputs: cooler pressure, condenser pressure, oil differential

pressure, cooler waterside differential pressure, and condenser

waterside differential pressure. See the Check Pressure

Transducers section (page 75) under Scheduled Maintenance.

These 5 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.

RESET

EXIT

Relieve all refrigerant pressure or drain the water before

replacing the temperature sensors.

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Carrier 19XR Spécifications Page 76

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