Lennox Merit Series Installation Instructions Manual page 16

DEMAND DEFROST CONTROL (A108) DIAGNOSTIC LEDS
The state (Off, On, Flashing) of two LEDs on the demand defrost control (DS1 [Red] and DS2 [Green]) indicate diagnostics
conditions that are described in table 3.
DS1 and DS2 System Status, Fault and Lockout Codes
DS2 DS1
Type
Green Red
OFF OFF Status
Simultaneous SLOW
Status
Flash
Alternating SLOW
Status
Flash
Simultaneous FAST
Fault
Flash
Alternating
Fault
FAST Flash
ON ON Fault
SLOW
OFF Fault
Flash
OFF ON Lockout
SLOW
OFF Fault
Flash
ON OFF Lockout
SLOW
ON Fault
Flash
ON Lockout
sh
Fast
OFF Fault
Flash
Fast
OFF Lockout
Flash
(Each fault adds 1 strike to that code's counter; 5 strikes per code = LOCKOUT)
Field Operation Checklist for Two-Stage Modulation Compressors
Unit Readings
Compressor
Voltage
Amperage
Outdoor Unit Fan Motor
Amperage
Temperature
Ambient
Outdoor Coil Discharge Air
Compressor Discharge Line
Indoor Return Air
Indoor Coil Discharge Air
Pressures
Suction (Vapor)
Liquid
DEMAND DEFROST CONTROL (A108) DIAGNOSTIC LEDS
Condition/Code
Power problem
Normal operation
5-minute anti-short cycle delay
Ambient Sensor Problem
Coil Sensor Problem
Demand Defrost Control Failure
Low Pressure Fault
Low Pressure Lockout
High Pressure Fault
High Pressure Lockout
Discharge Line Temperature Fault
Discharge Line Temperature
Lockout
Discharge Sensor Fault
Discharge Sensor Lockout
Y1 - First Stage
TABLE 3
Possible Cause(s)
No power (24V) to demand defrost
control terminals R and C or demand
defrost control failure.
Unit operating normally or in standby
mode.
Initial power up, safety trip, end of
room thermostat demand.
Sensor being detected open or shorted or out of temperature range. Demand defrost control
will revert to time/temperature defrost operation. (System will still heat or cool).
Sensor being detected open or shorted or out of temperature range. Demand defrost control
will not perform demand or time/temperature defrost operation. (System will still heat or cool.)
Indicates that demand defrost control has internal component failure. Cycle 24VAC power to
demand defrost control. If code does not clear, replace demand defrost control.
Restricted air flow over indoor or
outdoor coil.
Improper refrigerant charge in
system.
Improper metering device
installed or incorrect operation
of metering device.
Incorrect or improper sensor
location or connection
system.
This code detects shorted sensor or high discharge temperatures. If the discharge line
temperature exceeds a temperature of 285ºF (140ºC) during compressor operation, the
demand defrost control 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 225ºF (107ºC).
The demand defrost control 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 demand defrost control will count
one fault. After 5 faults, the demand defrost control will lock out.
Expected results during Y2 demand
(Toggle switch On)
Same
Higher
Same or Higher
Same
Higher
Higher
Same
Lower
Lower
Higher
Page 16
Solution
1.
Check control transformer power (24V).
2.
If power is available to demand defrost control and
trol.
None required.
None required (jumper TEST pins to override)
Remove any blockages or restrictions from coils
and/or fans. Check indoor and outdoor fan
motor for proper current draws.
Check system charge
method.
Check system operating
compare to unit subcooling tables in this
instruction or located on unit access panel.
Make sure all pressure switches and sensors
have secure connections to system to prevent
to
refrigerant leaks or errors in pressure and
temperature measurements.
Y2 - Second Stage
using subcooling
pressures and