50A51 Flow Chart 1 - American Standard *UD Series Operation Manual

50A51 Flow Chart 1

Inducer Blower
Check
1B
YES
Is LED
light on control
ON or flashing?
(Door switch
closed)
NO
Is 120V
YES
present across
control terminals
LINE & LINE
NEUTRAL?
NO
Correct 120V
power supply.
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.
1A
Place
Does indoor
thermostat fan
blower run at
switch in the
HEAT speed?
ON position.
YES
Is 24V
present at present at
control terminals control terminals
R & B/C?
NO
Replace control.
Check for operation.
Is 120V
YES
present across
present across
control terminals
primary of control
XFMR & XFMR
transformer?
NEUTRAL?
Repair wiring
to transformer.
Check operation.
YES
Return fan
switch to AUTO
position.
NO
YES
Is 120V
Is 24V
present at
control terminals
HEAT & CIR
G & B/C?
NEUTRAL?
NO
YES
Is 120V Is 120V
present across
secondary of
transformer?
NO
Replace transformer.
Check operation.
Note: Check diagnostic LED light flash rate through view
port in blower door before removing blower door!
56
YES
Indoor blower
fault. Repair or replace.
Check for operation.
NO
Replace control.
Check for operation.
Replace control.
Check for operation.
YES
Is 24V
present across
12 pin connector pins
TH & TR on the
control?
NO NO
Repair wiring and/or
plug connection.
Check operation.
YES