Page 24
505328M 06/09
TEST
See Figure 33 for details concerning Test Mode
operations.
NORMAL
The DCB monitors the O line, to determine the system
operating mode (heat/cool), outdoor ambient temperature,
coil temperature (outdoor coil) and compressor run time to
determine when a defrost cycle is required.
CALIBRATION
The DCB is considered uncalibrated when power is
applied to the DCB, after cool mode operation, or if the coil
temperature exceeds the termination temperature when it
is in heat mode.
DEFROST
For detail information on DEFROST MODE, see
Detail
Defrost Mode Operation
on page 26.
Table 16. DCB Diagnostic LEDs
DS2
Green
DS1
Red
Condition
Possible Cause(s)
Solution
OFF
OFF
Power problem
No power (24V) to DCB terminals R and
C or DCB failure.
1
Check control transformer power (24V).
2
If power is available to DCB and LED(s) do not light,
replace DCB.
SIMULTANEOUS
SLOW FLASH
Normal operation
Unit operating normally or in standby
mode.
None required.
ALTERNATING
SLOW FLASH
5−minute anti−short cycle delay
Initial power up, safety trip, end of room
thermostat demand.
None required (Jumper TEST pins to override)
SIMULTANEOUS
FAST FLASH
Ambient sensor problem
Sensor being detected open or shorted or out of temperature range. DCB will revert to
time/temperature defrost operation. (System will still heat or cool).
ALTERNATING
FAST FLASH
Coil sensor problem
Sensor being detected open or shorted or out of temperature range. DCB will not perform demand
or time/temperature defrost operation. (System will still heat or cool).
ON
ON
DCB failure
Indicates that DCB has internal component failure. Cycle 24 volt power to DCB. If code does not
clear, replace DCB.
FAULT and LOCKOUT CODES
(
Each fault adds 1 strike to that code’s counter; 5 strikes per code = LOCKOUT
)
OFF
SLOW
FLASH
Low pressure fault
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.
1
Remove any blockages or restrictions from coils
and/or fans. Check indoor and outdoor fan motor for
proper current draws.
2
Check system charge using approach and
subcooling temperatures.
3
Check system operating pressures and compare to
unit charging charts.
4
Make sure all pressure switches and sensors have
secure connections to system to prevent refrigerant
leaks or errors in pressure and temperature
measurements.
OFF
ON
Low pressure lockout
SLOW
FLASH
OFF
High pressure fault
ON
OFF
High pressure lockout
Units WITH Discharge Line Sensor
SLOW
FLASH
ON
Discharge line temperature
fault
This code detects shorted sensor or high discharge temperatures. If the discharge line temperature
exceeds a temperature of 300ºF (148ºC) 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 225ºF (107ºC).
FAST
FLASH
ON
Discharge line temperature
Lockout
OFF
FAST
FLASH
Discharge sensor fault
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.
FAST
FLASH
OFF
Discharge sensor lockout
Units WITHOUT Discharge Line Sensor
SLOW
FLASH
ON
Discharge line temperature
fault
Some heat pump units do not use a defrost line sensor. Therefore this code is not applicable.
FAST
FLASH
ON
Discharge line temperature
lockout
OFF
FAST
FLASH
Discharge sensor fault
Some heat pump units do not use a defrost line sensor. However, on these units a resistor is
installed across pins P4−1 and P4−2. If the resistor is missing or damaged then this fault code will
be displayed.
FAST
FLASH
OFF
Discharge sensor lockout
Some heat pump units do not use a defrost line sensor. Therefore this code is not applicable.
