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Fujitsu FO20R Series Installation Instructions Manual page 64

Variable speed r-410a heat pump outdoor units
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9.0 DIAGNOSTICS & TROUBLESHOOTING
9.10 Checking Transducers & Temperature Sensors (cont.)
TEMPERATURE SENSORS:
All the temperature sensors/thermistors used in
the equipment use the same scale of 10,000 Ohms
at 77ºF (25ºC). This means, a sensor exposed to
77ºF will show a resistance of 10,000 Ohms +/-
1%. As the temperature decreases, the resistance
increases. Alternatively, as the temperature
increases, the resistance decreases.
Measurements will be made with the sensor
disconnected from the control board. Again,
comparing the results must be done against a
calibrated tester.
A glass of water, mixed completely with ice
chips and given several minutes to settle should
measure 32 to 32.4ºF.
64
Apply resistance measurements to the chart found
below and compare to the control.
32º will have a resistance +/- 1% of 32,650 Ohms.
In the event Celsius is being used, the Fahrenheit
temperature will need to be converted.
ºC = (ºF - 32) * 5 / 9
Example using 82ºF
ºC = (82 - 32) * 5 / 9
ºC = (50) * 5 / 9
ºC = 250 / 9
ºC = 27.8

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