Installation Manual

11 421 01 5900 02
Specifications subject to change without notice.
Refer to Table 4 and Fig. 18 and 19 for resistance values versus
temperature.
Table 4 – 10K/50Kohm Resistance Values vs Temperature
10Kohms
_C(_F)
TEMPERATURE RESISTANCE (Kohms)
25.0 (77.0) 10.0 + / - 2.3%
0.0 (32.0) 32.6 + / - 3.2%
-28.0 (-18.4) 85.5 + / - 3.4%
50Kohms
125.0 (257.0) 1.7 + / - 1.6%
75.0 (167.0) 7.40 + / - 2.0%
25.0 (77.0) 50.0 + / - 2.3%
A91431
Fig. 18 - 10K Thermistor Resistance Versus T emperature
0
50
100
150
200
250
300
350
400
450
020406080100120
RESISTANCE (KOHMS)
TEMPERATURE (°°F)
50K THERMISTOR
A14022
Fig. 19 - 50K Thermistor Resistance Versus T emperature
If the outdoor air or coil thermistor should fail, the control will
flash the appropriate fault code (see Table 6).
IMPORTANT: The outdoor air thermistor, coil thermistor and
suction thermistor should be factory mounted in the final
locations. Check to ensure thermistors are mounted properly
(See Fig. 20, 21, 22 and 23).
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:
S In cooling if the outdoor air sensor indicates  10_F( 5.6_C)
warmer than the coil sensor (or) the outdoor air sensor indicates
 25_F( 12_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 comparisons are not performed during low ambient
cooling.
Outdoor Coil Thermistor
The outdoor coil thermistor is a 10Kohm resistor used for multiple
system operations. It provides the coil/liquid line temperature to
the AC unit board and Observer
®
Wall Control. Low ambient
operation, and assistance with OAT temperature measurement are
some of the functions. The sensor must be securely mounted to the
tube connecting the coil and distributor. See Fig. 21 for proper
placement. See Table 4 for proper resistances.
A14328
Fig. 20 - Outdoor Coil Thermistor (OCT) Attachment
(On Distributor Tube)
A11142
Fig. 21 - OAT Thermistor Location (Bottom of Control Box)
Suction Thermistor (OST)
Suction Thermistor is used to accurately measure suction
temperature and must be secured on the suction tube and aligned
longitudinally to the vertical surface of the tube axis (see Fig. 22).
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment
damage or improper operation.
In order to minimize the ambient influence, make sure the
thermistor curved surface hugs the pipe surface and is
secured tight using the wire tie fished through the original
slot insulating polymer body.