50A50 Flow Chart 4 - American Standard *UD Series Operation Manual

50A50 Flow Chart 4

Main burner
ignition check
Inducer ON.
YES
Replace ignitor.
Check operation.
YES
Replace broken or
defective wiring.
Check operation.
Note: Diagnostic indicator
may indicate two flashes with
a pause due to loss of flame
condition (lock out). Inducer
motor and indoor blower will be
energized continuously.
Note: Read diagnostic indicator
information provided on
control label.
CAUTION: If diagnostic indicator (LED) shows five (5) flashes,
turn off gas supply at source before disconnecting electrical power.
Failure to do so may result in personal injury or fire.
4A
4E
Diagnostic
LED flashing
fast (2 times per
sec.) continously.
4B
Turn power OFF to
furnace. Unplug ignitor
from wire harness.
Connect voltemeter across
ignitor wiring harness
leads from control.
Energize system.
Turn manual knob to
OFF position. Connect
manometer to outlet
pressure tap. Turn knob
4C
Is 120V
present at
ignitor leads?
4D
Is 120V
present at
control terminals
IGN & IGN
NEUTRAL?
NO
gas valve leads after
Replace control.
Check operation.
YES
Does ignitor
Does burner
warm up and
glow?
NO
4F
Is gas NO
valve manual
knob in ON
position?
YES
to ON position.
Energize system.
4I
4H
YES
Refer to service
Is outlet
facts or installers
pressure detected
guide for proper
after ignitor warm
pressure settings.
up time?
NO
4K
NO
Is gas at
source?
YES
4L
Connect
voltemeter to
gas valve leads.
Energize system.
4M 4N
Is 24V NO
detected across present across
control MV terminals
ignitor warm after ignitor
up time? warm up?
YES
Replace gas Repair or
replace broken
valve. Energize
leads to gas valve.
system. Check
Check operation.
operation.
Note: Check diagnostic LED light flash rate through view
port in blower door before removing blower door!
54
YES
ignite?
NO
Repair low
voltage wiring
fault. Check
operation.
Repair low
voltage wiring
fault. Check
operation.
4J
Is manifold
pressure adjusted
to required
setting?
Replace pressure
switch. Check
operation.
Restore gas
supply at source.
Check operation.
Is 24V
NO
Replace control
module. Check
operation.
YES
YES
NO