Control Board Troubleshooting Guide - Lennox F8AUH series Service Manual

VIII-Troubleshooting- Silicon Carbide Ignition System
PROBLEM: 1 UNIT FAILS TO OPERATE IN THE COOLING, HEATING, OR CONTINUOUS FAN MODE
Condition
1.1
− Both diagnostic lights fail to light up.
LED#1−Off
LED#2−Off
1.2
- Diagnostic lights flash the roll-out
code. code.
LED#1-On, LED#1 O
LED#2 Slow Flash LED#2-Slow Flash
1.3
− On initial power−up the comb. air
blower does not energize. blower does not energize.
− Diagnostic lights flash the reverse
polarity code.
LED#1−Fast Flash,
LED#2−Slow Flash.
1.4
− On initial power up the combustion
air blower does not energize.
− Diagnostic lights flash normal power
on operation. on operation.
LED#1−Slow Flash
LED#2−Slow Flash
Possible Cause
1.1.1
Main voltage 120V not supplied to
unit.
1.1.2
Miswiring of furnace or improper
connections.
1.1.3
Circuit breaker tripped or fails to
close.
1.1.4
Door interlock switch failure.
1.1.5
Transformer Failure.
1.1.6
Failed control board.
1.2.1
Roll−out switch open.
1.2.2
Roll−out switch failure.
1.2.3
Miswiring or improper connections at Miswiring or improper connections at
roll−out switch.
1.2.4
Nine pin connector failure
1.3.1
120V main power polarity reversed.
1.4.1
Open combustion air blower motor
circuit.
1.4.2
Failed combustion air blower motor.
Page 23
Corrective Action / Comments
ACTION 1 − Check 120V main voltage.
Determine cause of main power failure.
ACTION 1 − Check for correct wiring of 120V to
power make up box and transformer.
ACTION 2 − Check 24V wiring to control board.
ACTION 1 − Replace circuit breaker if it is reset
but does not have continuity.
ACTION 2 − If circuit breaker still trips, check for
short.
ACTION 1 − Check that door switch is activated
when door is closed.
ACTION 2 − Check wire connections to switch, re-
place loose connectors.
ACTION 3 − Check continuity of switch in closed
position. Replace if malfunctioning
ACTION 1 − Check that transformer output is
24V. Replace if malfunctioning
ACTION 1 − If all the above items have been
checked, replace board.
ACTION 1 − Manually reset the roll−out switch
by pushing the top button.
ACTION 2 − Determine the cause of the roll−out
switch activation before leaving furnace.
ACTION 1 − Check continuity across roll−out
switch. Replace roll−out switch if switch is reset
but does not have continuity.
ACTION 1 − Check wiring connections to switch. ACTION 1 − Check wiring connections to switch
ACTION 1 − Check 9−pin connector for proper
connection to control board.
ACTION 2 − Check continuity of the multi plug
pin.
ACTION 1 − Check the 120V has line and neutral
correctly input into control.
ACTION 2 − Reverse the line and neutral at the
120V field connection. 120V field connection.
ACTION 1 − Check for 120V to combustion air
blower. If no power, check wire and connec-
tions.
ACTION 1 − If power is present at blower, replace
blower.