HP - D 4
Sensor Tests
Testing the liquid line temperature sensor
Introduction
The liquid line temperature sensor (Fig-
ure 9) is a negative coefficient type
thermister that changes electrical re-
sistance with changes in temperature.
When the temperature it senses drops,
the resistance of the sensor will in-
crease. When the temperature it
senses rises, the resistance of the
sensor will decrease.
Testing voltage across temperature sensor
This test is performed at the Comfort Assist control
board. The outdoor unit board must be on for this test.
Step 1
Measure the temperature of the liquid line (Figure 10).
Step 2
Measure the DC voltage across the pins at plug J8
(Figure 11.) Compare the voltage to the values shown
in Table 3. The voltage should approximate these val-
ues. If the voltage measured is not approximate to the
values listed in the table, replace the sensor.
Ohm meter
Step 1
Shut power to the unit off.
Step 2
Unplug the liquid line sensor from plug J8 (Figure 12).
Figure 10
Figure 9
Figure 11
Table 3
Figure 12
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