Carrier 19XL TROUBLESHOOTING GUIDE Overview , Checking the Display Messages , Checking Temperature Sensors , Checking Pressure Transducers

TROUBLESHOOTING GUIDE

Overview — The PIC has many features to aid the

operator and the technician in troubleshooting a 19XL

chiller.

• Byusing 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

viewthe chiller conditions at the time of alarm. The Status

tableswill 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

screensof 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.

• TheControl Test feature allows proper operation and test-

ingof 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

showthe required temperatures and pressures during these

operations.

• Other Service menu tables 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 LID default screen. A more

detailed message — along with a diagnostic message —

also is stored into the Alarm History table.

Checking the Display Messages — The ﬁrst area

to check when troubleshooting the 19XLis the LID display.

If the alarm light is ﬂashing, check the primary and second-

arymessage lines on the LID default screen (Fig. 13). These

messageswill 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 ﬂash 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-

ditionexisting, unless the alarm type is an unauthorized start

or a failure to shut down.

Checking Temperature Sensors — 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 Tables10A or 10B.

RESISTANCE CHECK —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 Tables10A or 10B. Check the resistance of both wires to

ground. This resistance should be inﬁnite.

VOLTAGEDROP — Using a digital voltmeter, the voltage

drop across any energized sensor can be measured while

thecontrol 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,

connectorplugs, 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 — 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).

SeeFig. 8 for sensor locations. The sensors are immersed

directlyin 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.

DUALTEMPERATURE SENSORS — 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

commonline. To use the second sensor, move the wire from

the number 1 position to the number 3 position.

Checking Pressure Transducers — 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:Wheneverthe oil pressure or the cooler

pressuretransducer 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-

erationgage. These readings are all viewed or calibrated from

theStatus01 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). Tocalibrate 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

isnot 0 psi (0 kPa), but within ± 5 psi (35 kPa), the value

may be zeroed by pressing the SELECT softkey while

thehighlight bar is located on the transducer, and then by

pressing the ENTER . The value will now go to zero.