Lennox XP14 SERIES Unit Information page 4

2 − Dual Capacitor C12
The compressor and fan in XP14 series units use permanent
split capacitor motors. The capacitor is located inside the unit
control box (see figure 2). A single dual" capacitor (C12) is
used for both the fan motor and the compressor (see unit wir-
ing diagram). The fan side and the compressor side of the ca-
pacitor have different MFD ratings. See side of capacitor for
ratings.
3 − Defrost System (CMC1)
The demand defrost control measures differential temper-
atures to detect when the system is performing poorly be-
cause of ice build−up on the outdoor coil. The controller
self−calibrates" when the defrost system starts and after
each system defrost cycle. The defrost control compo-
nents are shown in figure 4.
The control monitors ambient temperature, outdoor coil
temperature, and total run time to determine when a de-
frost cycle is required. The coil temperature probe is de-
signed with a spring clip to allow mounting to the outside
coil tubing. The location of the coil sensor is important for
proper defrost operation.
NOTE − The demand defrost control accurately measures
the performance of the system as frost accumulates on the
outdoor coil. This typically will translate into longer running
time between defrost cycles as more frost accumulates on
the outdoor coil before the board initiates defrost cycles.
Diagnostic LEDs
The state (Off, On, Flashing) of two LEDs on the defrost
board (DS1 [Red] and DS2 [Green]) indicate diagnostics
conditions that are described in table 2.
TEST PINS
DEFROST
TERMINATION
PIN SETTINGS
SENSOR
PLUG IN
(COIL & AM-
BIENT
SENSORS)
DELAY
PINS
REVERSING
VALVE
PRESSURE
SWITCH CIRCUIT
CONNECTIONS
NOTE − Component Locations Vary by Control Manufacturer.
Y2 not used on XP14
FIGURE 4
Defrost Control Pressure Switch Connections
The unit's automatic reset pressure switches (LO PS − S87
and HI PS − S4) are factory−wired into the defrost control on
the LO−PS and HI−PS terminals, respectively.
Low Pressure Switch (LO−PS) When the low pressure
switch trips, the defrost control will cycle off the compressor,
and the strike counter in the control will count one strike.
The low pressure switch is ignored under the following con-
ditions:
during the defrost cycle and 90 seconds after the termina-
tion of defrost
when the average ambient sensor temperature is below
15° F (−9°C)
for 90 seconds following the start up of the compressor
during "test" mode
High Pressure Switch (HI−PS) When the high pressure
switch trips, the defrost control will cycle off the compressor,
and the strike counter in the control will count one strike.
Defrost Control Pressure Switch Settings
High Pressure (auto reset) − trip at 590 psig; reset at 418.
Low Pressure (auto reset) − trip at 25 psig; reset at 55.
5−Strike Lockout Feature
The internal control logic of the control counts the pressure
switch trips only while the Y1 (Input) line is active. If a pres-
sure switch opens and closes four times during a Y1 (Input),
the control logic will reset the pressure switch trip counter to
zero at the end of the Y1 (Input). If the pressure switch
opens for a fifth time during the current Y1 (Input), the con-
trol will enter a lockout condition.
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 and 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 control through a field-re-
placeable harness assembly that plugs into the board.
LOW
Through the sensors, the control detects outdoor ambient
AMBIENT
THERMOSTAT
and coil temperature fault conditions. As the detected tem-
PINS
perature changes, the resistance across the sensor
changes. Figure 5 shows how the resistance varies as the
temperature changes for both type of sensors. Sensor re-
DIAGNOSTIC
LEDS
sistance values can be checked by ohming across pins
shown in table 1.
24V TERMINAL
STRIP
CONNECTIONS
Sensor
Outdoor
(Ambient)
Coil
Discharge (if
applicable)
Note: Sensor resistance decreases as sensed temperature increases
(see figure5).
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 1, may be performing as de-
signed. However, if a shorted or open circuit is detected,
then the sensor may be faulty and the sensor harness will
needs to be replaced.
Page 4
TABLE 1
Temperature Resistance values
Range °F (°C) range (ohms)
−35 (−37) to 120 280,000 to 3750
(48)
−35 (−37) to 120 280,000 to 3750
(48)
24 (−4) to 350 41,000 to 103
(176)
Pins/Wire
Color
3 & 4
(Black)
5 & 6
(Brown)
1 & 2
(Yellow)