18
TROUBLESHOOTING INFORMATION: UNITARY DIAGNOSTIC CODES
Diagnostic/Status LED Codes
ComfortNet™
Thermostat Only
Symptoms of Abnormal
Operation (Legacy &
ComfortNet™ Thermostat)
Green
Yello
w
Red Red Y1
Fault
Description
Message Code
Possible Causes
Corrective Actions Notes & Cautions
x Integrated control module
diagnostic/status LED’s display
the indicated code.
x ComfortNet™ thermostat
displays ‘---‘ in the temperature
display area.
1 Flash ON OFF ON if call
present;
OFF if no
call
x Outdoor air
temp sensor
fault.
AIR
SENSOR
FLT
A2
x Shorted sensor.
x Open sensor.
x Sensor disconnected.
x Sensor out of range.
x Check sensor
connection.
x Replace
open/shorted
sensor.
x Turn power OFF
prior to repair.
x Replace with correct
replacement part..
x Heat pump fails to operate in
heating mode.
x Integrated control module
diagnostic/status LED’s display
the indicated code.
x ComfortNet™ thermostat “Call for
Service” icon illuminated.
x ComfortNet™ thermostat scrolls
“Check Heat Pump” message.
2 Flashes ON OFF ON if call
present;
OFF if no
call
x Outdoor coil
temp sensor
fault.
COIL
SENSOR
FLT
A3
x Shorted sensor.
x Open sensor.
x Sensor disconnected.
x Sensor out of range.
x Check sensor
connection.
x Replace
open/shorted
sensor.
x Turn power OFF
prior to repair.
x Replace with correct
replacement part.
x Air conditioner/heat pump fails to
operate.
x Integrated control module
diagnostic/status LED’s display
the indicated code.
5 Flashes ON OFF OFF
x Open fuse.
BLOWN
FUSE
E5
x Short in low voltage
wiring.
x Locate and correct
short in low voltage
wiring.
x Turn power OFF
prior to repair.
x Replace fuse with 3-
amp automotive
type.
x Air conditioner/heat pump fails to
operate.
x Integrated control module
diagnostic/status LED’s display
the indicated code.
6 Flashes ON OFF OFF
x Board miss-
operation.
INTERNAL
FAULT
EE
x Compressor relay
contacts welded.
x Replace control. x Turn power OFF
prior to repair.
x Replace with correct
replacement part.
x Air conditioner/heat pump fails to
operate.
x Integrated control module
diagnostic/status LED’s display
the indicated code.
x ComfortNet™ thermostat “Call for
Service” icon illuminated.
x ComfortNet™ thermostat scrolls
“Check Air Conditioner” or
“Check Heat Pump” message.
7 Flashes ON OFF ON if call
present;
OFF if no
call
x Circulator
blower motor
is not
running
when it
should be
running.
MOTOR
NOT RUN
b0
x Indoor blower motor
problem.
x Communications error
between indoor and
outdoor unit.
x Check indoor
blower motor.
x Check indoor
blower motor
wiring.
x Check indoor unit
control.
x Repair/ replace any
faulty wiring.
x Repair/ replace
indoor blower
motor or control.
x Turn power OFF
prior to repair.
x Applies only to fully
communicating
system using
ComfortNet™
thermostat.
x Replace with correct
replacement part.
x Air conditioner/heat pump
operates at reduced
performance.
x Air conditioner/heat pump
operating at low stage when
expected to operate at high
stage.
x Integrated control module
diagnostic/status LED’s display
the indicated code.
8 Flashes ON OFF ON if call
present;
OFF if no
call
x Airflow is
lower than
demanded.
LOW ID
AIRFLOW
b9
x Indoor blower motor
problem.
x Blocked filters.
x Restrictive/ undersized
ductwork.
x Indoor/ outdoor unit
miss-match.
x Check indoor
blower motor.
x Check filters;
clean/replace as
needed.
x Check ductwork;
resize as needed.
x Verify indoor and
outdoor units are
properly matched.
x Turn power OFF
prior to repair.
x Applies only to fully
communicating
system using
ComfortNet
thermostat.
x Replace with correct
replacement part.
x See specification
sheet(s) for airflow
requirements and
maximum external
static pressure.
x See specification
sheets for approved
system matches.
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