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a digital ohmmeter. The resistance and corresponding temperature is listed in Table 11A or
Table 11B. Check the resistance of both wires to ground. This resistance should be infinite.
Voltage Drop
Using a digital voltmeter, the voltage drop across any energized sensor can be measured
while the control is energized. Table 11A or Table 11B lists the relationship 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.
Check Sensor Accuracy
Place the sensor in a medium of a 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).
CAUTION
CAUTION
!
Relieve all refrigerant pressure or drain the water prior to replacing the tempera-
ture sensors.