Lennox Elite Series Installation Instructions Manual page 22

The 5-strike pressure switch lockout condition can be reset
by cycling OFF the 24-volt power to the control board or by
shorting the TEST pins between 1 to 2 seconds. All timer
functions (run times) will also be reset.
If a pressure switch opens while the Y1 Out line is
engaged, a 5-minute short cycle will occur after the switch
closes.
DEFROST SYSTEM SENSORS
Sensors connect to the defrost board through a
field-replaceable harness assembly that plugs into the
board as illustrated in figure 39 on page 23. Through the
sensors, the board detects outdoor ambient, coil, and
discharge temperature fault conditions. As the detected
temperature changes, the resistance across the sensor
changes. Sensor resistance values can be checked by
ohming across pins shown in table 11.
Table 11. Sensor Temperature/Resistance Range
Pins/W
Temperature Resistance values ire
Sensor Range °F (°C) range (ohms) Color
Outdoor -35 (-37) to 120 (48) 280,000 to 3750 3 & 4
(Black)
Coil -35 (-37) to 120 (48) 280,000 to 3750 5 & 6
(Brown)
Discharge (if 24 (-4) to 350 (176) 41,000 to 103 1 & 2
applicable) (Yellow)
Note: Sensor resistance increases as sensed temperature decreases.
Figure 37 shows how the resistance varies as the
temperature changes for both type of sensors.
NOTE - When checking the ohms across a sensor, be
aware that a sensor showing a resistance value that is not
within the range shown in table 11, maybe performing as
designed. However, if a shorted or open circuit is detected,
then the sensor may be faulty and the sensor harness will
need to be replaced.
1 ml157_O
I
mMm7450
19275
11775
B 15425
_ 19975
26200
[] 34375
mm46275
I 62700 85300
i
10000 30000 50000 70000 90000
RESISTANCE (OHMS)
Figure 37. Temperature/Resistance Chart
(Ambient and Coil Sensors)
m
m250
roll
m325
m
m425
m
m600
m
m825
m1175
WOO
_025
"500
3000
3750
4650 5825
1000 2000 3000 4000 5000 6000
RESISTANCE (OHMS)
Figure 38. Temperature/Resistance Chart
(Discharge Sensor)
Ambient Sensor--The ambient sensor considers
outdoor temperatures below -35°F (-37°C) or above 120°F
(48°C) as a fault. 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.
Coil Sensor--The coil temperature sensor considers
outdoor temperatures below -35°F (-37°C) or above 120°F
(48°C) as a fault. If the coil temperature sensor is detected
as being 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 fault condition.
Discharge Line Sensor--If the discharge line
temperature 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:
.
,
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").
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").
505329M 04/08
Page 22