Lennox Signature Collection XP15 Installation Instructions Manual page 25

Table 16. DCB Diagnostic LEDs
DS2 DS1
Condition Possible Cause(s) Solution
Green Red
1 Check control transformer power (24V).
No power (24V) to DCB terminals R and 2 If power is available to DCB and LED(s) do not light,
OFF OFF Power problem C or DCB failure.
replace DCB.
SIMULTANEOUS Unit operating normally or in standby None required.
SLOW FLASH Normal operation mode.
ALTERNATING Initial power up, safety trip, end of room None required (Jumper TEST pins to override)
SLOW FLASH 5-minute anti-short cycle delay thermostat demand.
SIMULTANEOUS Sensor being detected open or shorted or out of temperature range. DCB will revert to
FAST FLASH Ambient sensor problem time/temperaturedefrost operation. (System will still heat or cool).
ALTERNATING Sensor being detected open or shorted or out of temperature range. DCB will not perform demand
FAST FLASH Coil sensor problem or time/temperature defrost operation. (System will still heat or cool).
ON Indicates that DCB has internal component failure. Cycle 24 volt power to DCB. If code does not
ON DCB failure clear, replace DCB.
FAULT and LOCKOUT CODES
(Each fault adds 1 strike to that code's counter; 5 strikes per code = LOCKOUT)
1 Remove any blockages or restrictions from coils
SLOW
OFF FLASH Low pressure fault
OFF ON Low pressure lockout
SLOW
FLASH OFF High pressure fault
ON OFF High pressure lockout
1 Restricted air flow over indoor or out-
door coil.
2 Improper refrigerant charge in sys-
tem.
3 Improper metering device installed or
incorrect operation of metering de-
vice.
4 Incorrect or improper sensor location
or connection to system.
2
3
4
and/or fans. Check indoor and outdoor fan motor for
proper current draws.
Check system charge using approach and
subcooling temperatures.
Check system operating pressures and compare to
unit charging charts.
Make sure all pressure switches and sensors have
secure connections to system to prevent refrigerant
leaks or errors in pressure and temperature
measurements.
SLOW Discharge line temperature
FLASH ON fault
FAST
FLASH ON
FAST
OFF FLASH
FAST
FLASH OFF
Discharge line temperature
Lockout
Discharge sensor fault
Discharge sensorlockout
This code detects shorted sensor or high discharge temperatures. 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).
The board detects open sensor or out of temperature sensor range. This fault is detected by allow-
ing 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.
SLOW Discharge line temperature
FLASH ON fault
FAST Discharge line temperature
FLASH ON lockout
FAST
FLASH
OFF
Some heat pump units do not use a defrost line sensor. Therefore this code is not applicable.
Some heat pump units do not use a defrost line sensor. However, on these units a resistor is
OFF Discharge sensor fault installed across pins P4-1 and P4-2. If the resistor is missing or damaged then this fault code will
be displayed.
FAST Discharge sensor lockout
FLASH Some heat pump units do not use a defrost line sensor. Therefore this code is not applicable.
Page 25
XP15 SERIES