50A51 Flow Chart 4 - American Standard *UD Series Operation Manual

50A51 Flow Chart 4

4A
Flame Sensor
Check
De-energize system.
Disconnect 12 pin
connector. Connect
ohmeter from flame
Disconnect flame
Is
NO
sensor from wire.
resistance less
Measure continuity
than 50 megohms
from wire end to FP
(50,000,000
ohms)?
YES
Disconnect lead
from flame sensor.
Connect ohmeter
from sensor to
burner ground.
wire. Energize system.
Check operation.
NO
Is resistance
less than 50
megohms?
YES
Replace sensor.
Energize system. sensor lead. Check
Check operation.
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.
4D
YES
Does ignitor
Does main
remain energized
burner remain
with flame
lit?
present?
NO
sensor pin FP to
burner GROUND.
4C
Disconnect AC power to
system at main fuse or
circuit breaker. Connect
volt meter from control
term LINE NEUTRAL to
pin on 12 pin
BURNER GROUND.
connector.
Energize module.
4B
YES
Is control
Is sensor ground wire
lead good? connected to burner
ground?
NO
Connect ground wire
Repair or replace
from burner to 12 pin con-
nector terminal GROUND.
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.
Replace flame
operation.
Blower
NO
at heat speed
within one minute of
burner ignition?
NO
YES
Is 120V
present at control
term. HEAT & CIR.
NEUTRAL?
NO
Is 120V
present at
burner ground?
NO
YES
Connect a micro
ammeter in series
with flame sensor
and sensor lead.
Energize system.
Measure current
when burner ignites.
NO
Is 1 microamp
or more present?
YES
Replace control.
Check operation.
Note: Check diagnostic LED light flash rate through view
port in blower door before removing blower door!
59
YES
System is
functioning
properly.
YES
Repair wiring and/or
replace indoor blower
motor. Check
operation.
Replace control
module. Check
operation.
YES
Reverse 120V
LINE & NEUTRAL
wires. Energize system.
Check operation.
Clean surface of
flame sensor with fine
steel wool. Reinstall.
Check operation.
YES
NO Remove
sensor. Does
sensor have carbon
or dust buildup?
NO
Note: Read diagnostic indicator
information provided on control label.