Lennox Merit Series Installation Instructions Manual page 14

DEMAND DEFROST CONTROL (A108) INPUTS, OUTPUTS AND CONFIGURABLE SETTINGS
Control Control Label or
Locations Description
P1 50, 70, 90, 100
W1
C
L
P2
R
Y2
O
Y1
P3 55, 50, 45, 40
DIS-YEL
P4
AMB-BLACK
COIL-BROWN
P5 DELAY
P6 TST, PS DF, C, R, O, Y1, Y2
DS1 RED LED
DS2 GREEN LED
FAN TWO CONNECTORS
O OUT O OUT
LO-PS LO-PS
Y2 OUT Y2 OUT
Y1 OUT Y1 OUT
HS-PS HS-PS
L L
24V 24V
TABLE 2
Purpose
Defrost Temperature
Termination Shunt (Jumper)
Pins
24VAC Thermostat Input /
Output
24VAC Common
Thermostat Service Light
24VAC
Thermostat Input
Thermostat Input
Thermostat Input
Low Ambient Thermostat
Pins
Coil Sensor
Ambient Sensor
Discharge Sensor
Delay Mode
Factory Test Connectors
Diagnostic LED
Condenser Fan Operation
24 VAC output
Low-Pressure Switch
24 VAC Output
24 VAC Common Output
High-Pressure Switch
Service Light Output
24 Volt output
Page 14
Function
The demand defrost control (illustrated in figure 17) has selections which
are: 50, 70, 90, and 100°F (10, 21, 32 and 38°C). The shunt termination
pin is factory-set at 50°F (10°C). If the temperature shunt is not installed,
the default termination temperature is 90°F (32°C).
24VAC input / output from indoor thermostat to indoor unit.
24VAC common.
Thermostat service light connection.
24VAC.
Controls the second stage operation of the unit.
Reversing valve solenoid.
Controls the operation of the unit.
Provides selection of the Y2 compressor lock-in temperature. Valid
options are 40, 45, 50 and 55 degrees Fahrenheit.
(P4-5) Ground connection for outdoor coil temperature sensor.
(P4-6) Connection for outdoor coil temperature sensor.
(P4-3) Ground connection for outdoor ambient temperature sensor.
(P4-4) Connection for outdoor ambient temperature sensor.
No discharge sensor is used; replaced by 10K resistor.
The demand defrost control has a field-selectable function to reduce
occasional sounds that may occur while the unit is cycling in and out of
the defrost mode. When a jumper is installed on the DELAY pins, the
compressor will be cycled off for 30 seconds going in and out of the
defrost mode. Units are shipped with jumper installed on DELAY pins.
-
NOTE The 30-second off cycle is NOT functional when TEST pins on
P1 are jumpered.
No field use.
Demand defrost control LEDs may be OFF, ON, or FLASHING to
indicate diagnostic conditions which are described in table 3.
These two connections provide power for the condenser fan.
24 VAC output connection for reversing valve.
When the low pressure switch trips, the demand defrost control will cycle
off the compressor, and the strike counter in the demand defrost control
will count one strike. The low pressure switch is ignored under the
following conditions:
during the defrost cycle and 90 seconds after the termination of
defrost
when the average ambient sensor temperature is below 0°F (-18°C)
during 90 seconds following the start of the compressor
during TEST mode.
24 VAC output for second-stage compressor solenoid.
24 VAC common output, switched for enabling compressor contactor.
When the high pressure switch trips, the demand defrost control will cycle
off the compressor, and the strike counter in the demand defrost control
will count one strike.
24VAC service light output.
24VAC typically used to supply power to the Lennox System Operation
Monitor (LSOM). Not used in this system.