TEMPERATURE THERMISTORS
Thermistors are electronic devices which sense temperature. As the
temperature increases, the resistance decreases. Thermistors are
used to sense outdoor ambient (OAT) and coil temperature (OCT).
Refer to Fig. 8 for resistance values versus temperature. If the
outdoor ambient or coil thermistor should fail, the control will
flash the appropriate fault code (see Table 6 0
IMPORTANT: Outdoor air thermistor and coil thermistor are
factory mounted in the final locations. Check to insure thermistors
are mounted properly per Fig. 9 and Fig. 10.
Thermistor Sensor Comparison
The control continuously monitors and compares the outdoor air
temperature sensor and outdoor coil temperature sensor to ensure
proper operating conditions. The comparison is:
-- If the outdoor air sensor indicates 10°F (5.56°C) warmer
than the coil sensor (or) the outdoor air sensor indicates
20°F (11.11°C) cooler than the coil sensor, the sensors
are out of range.
-- If the sensors are out of range, the control will flash the
appropriate fault code as shown in Table 6.
-- The thermistor comparison is not performed during low
ambient cooling or defrost operation.
Failed Thermistor Default Operation
Factory defaults have been provided in the event of failure of
outdoor air thermistor and/or coil thermistor.
If the OAT sensor should fail, low ambient cooling will not be
allowed and the one minute outdoor fan-off delay will not occur.
If the OCT sensor should fail, low ambient cooling will not be
allowed.
OAT Thermistor must be locked in place with spherical nib end
facing towards" the front of the control box
THERMISTOR CURVE
9o _ _ T F
O 20 40 60 80 100 120
(-17.77) (-6.67) (4.44) (15.56) (26.67) (37.78) (48.89)
TEMPERATURE "F ('C)
Fig. 8 - Resistance Values Versus Temperature
A08054
OAT Thermistor must be
locked in place with spherical
nib end facing towards the
front of the control box
//
x" J ......... fl
\
Fig.9 - Outdoor Air Thermistor (OAT) Attachment
OCT Thermistor must be
tight on the liquid tube,
/
/
/
\\\
Fig. 10 - Outdoor Coil Thermistor (OCT) Attachment
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