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Ambient and Coil Sensor
Discharge Sensor
RESISTANCE
(OHMS)
RESISTANCE
(OHMS)
TEMPERA
TURE
(ºF)
TEMPERA
TURE (ºF)
5750
7450
9275
11775
15425
19975
26200
34375
46275
62700
200
325
250
425
600
825
1175
1700
2500
3750
5825
10
0
90
80
70
60
50
40
30
20
10
0
300
280
260
240
220
200
180
160
140
120
100
1000
0
3000
0
5000
0
7000
0
9000
0
1000
2000
5000
4000
6000
3000
4650
3000
2025
1400
1000
700
225
275
375
500
85300
Figure 25. Temperature/Resistance Chart
1.
Defrost Coil Sensor (RT21)
This sensor (see
mounting location in Figure 24, Detail B) considers
actual
coil temperatures
below −35°F (−37°C) or
above 120°F (48°C) to be a fault.
If the defrost coil sensor is open, shorted or out of the
temperature range of the sensor, the board will not
perform demand or time/temperature defrost
operation and will display the appropriate fault code.
Heating and cooling operation will be allowed in this
2.
Ambient Sensor (RT13)
This sensor (see
mounting location in Figure 24, Detail A) considers
outdoor temperatures
below −35°F (−37°C), or
above 120°F (48°C) as a fault condition.
If the ambient sensor is detected as being open,
shorted or out of the temperature range of the sensor,
the board will not perform demand defrost operation.
The board will revert to time/temperature defrost
operation and will display the appropriate fault code.
Heating and cooling operation will be allowed in this
fault condition.
3.
Discharge Line Sensor (RT28)
This sensor (see
mounting location in Figure 24, Detail C), which covers
a range of 150°F (65°C) to 350°F (176°C), is designed
to mount on a 1/2" refrigerant discharge line.
If this sensor exceeds a temperature of 300°F (148°C)
during compressor operation, the board will
de−energize the compressor contactor output (and the
defrost output, if active). The compressor will remain
off until the discharge temperature has dropped below
225°F (107°C) and the 5-minute anti−short cycle delay
has been satisfied. This sensor has two fault and
lockout codes:
A
If the board recognizes five high discharge line
temperature faults during a single (Y1)
compressor demand, it reverts to a lockout mode
and displays the appropriate code. This code
detects shorted sensor or high discharge
temperatures. Code on board is Discharge Line
Temperature Fault and Lockout.
B
If the board recognizes five temperature sensor
range faults during a single (Y1) compressor
demand, it reverts to a lockout mode and displays
the appropriate code. The board detects open
sensor or out-of-temperature sensor range. This
fault is detected by allowing the unit to run for 90
seconds before checking sensor resistance. If the
sensor resistance is not within range after 90
seconds, the board will count one fault. After five
faults, the board will lockout. Code on board is
Discharge Sensor Fault and Lockout.
