Lennox F8AUH series Service Manual page 28

PROBLEM 6: BURNERS LIGHT WITH HEATING DEMAND BUT UNIT SHUTS DOWN
6.5
− Combustion air blower energizes
with a heating demand.
− Burners light.
− Diagnostic lights flash watch guard
flame failure.
− NOTE" Unit might go into 60 min-
ute Watchguard mode depending on
intermittent nature of sensor signal.
LED#1−Alternating Slow Flash
LED#2−Alternating Slow Flash
PROBLEM 7: CONTROL SIGNALS LOW FLAME SENSE DURING HEATING MODE
Condition
7.0
− Unit operates correctly but the
diagnostic lights flash low flame
sense code. sense code
LED#1−Slow Flash
LED#2−Fast Flash
PROBLEM 8: INDOOR BLOWER FAILS TO OPERATE IN COOLING, HEATING, OR CONTINUOUS
Condition
8.0
− Indoor blower fails to operate in
continuous fan, cooling, or heating
mode.
Condition
9.0
− AM radio interference
PREMATURELY (CONT.)
Loose sensor wire connection
causes intermittent loss of flame sig-
Possible Cause
Sense rod is improperly located on
Sense rod is contaminated.
Possible Cause
Miswiring of furnace or improper con-
nections at control or indoor blower
120V is not being supplied to the in-
door air blower or blower motor fail-
Defective control board
PROBLEM 9: RF STATIC DURING TIME FOR IGNITION
Possible Cause
Ignitor operation
6.5.1
nal.
7.1.1
the burner.
7.1.2
FAN MODE
8.1.1
motor.
8.1.2
ure.
8.1.3
9.1.2
Page 28
ACTION 1 − Check that the sensor is properly lo-
cated.
ACTION 2 − Check that the sense wire is proper-
ly attached to both the sensor and the control.
Pay extra attention to the pin connectors.
Corrective Action/Comments
ACTION 1 − Check the sense rod for proper loca-
tion on the burner. Properly locate the sense rod
or replace if rod cannot be located correctly.
ACTION 1 − Check sense rod for contamination
or coated surface. Clean the sense rod with steel
wool or replace sensor. DO NOT USE SAND PA-
PER TO CLEAN ROD. SAND PAPER WILL
CONTRIBUTE TO THE CONTAMINATION
PROBLEM.
Corrective Action/Comments
ACTION 1− Correct wiring and/or replace any
loose connections. Check for correct wiring and
loose connections.
ACTION 1 − Check for 120V at the various calls
for indoor blower by energizing "Y", "G", and "W"
individually on the low voltage terminal strip.
Note that when "W' is energized, the blower is
delayed 45 seconds. If there is 120V to each mo-
tor tap but the blower does not operate, replace
the motor.
ACTION 1 − If there is not 120V when "Y", "G", or
"W" is energized, replace the control.
Corrective Action/Comments
−
ACTION 1 Call Technical Support, Dallas