50A50 Flow Chart 1 - American Standard *UD Series Operation Manual

50A50 Flow Chart 1

Indoor Blower
Check
1C 1D
YES
Is LED
light on control
ON or flashing?
(Door switch
closed)
NO
1G
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 Thermostat
in the on position.
1E
YES
Is 24V
present at
control terminals control terminals
R & B/C?
NO
Replace control.
Check for operation.
NO
1H 1I
Is 120V
YES
present at
present across
control terminals
primary of control
XFMR & XFMR
transformer?
NEUTRAL?
Correct 120V
power supply. Check
1B
YES
Does
indoor blower
run at HEAT
AUTO position.
speed?
NO
1F
Is 120V
YES
Is 24V
present at
present at
control terminals
HEAT & CIR
G & B/C?
NEUTRAL?
NO
1J
YES
Is 120V Is 24V
present across
secondary of
transformer?
NO
Replace
transformer. Check
operation. operation.
Note: Check diagnostic LED light flash rate through view
port in blower door before removing blower door!
51
Return
fan switch to
YES
Indoor blower
fault. Repair or
replace. Check
operation.
NO
Replace control.
Check for operation.
Repair wiring from
control to thermostat.
Check operation.
1K
Is 24V
YES
present across
12 pin connector pins
TH & TR on the
control?
NO NO
Repair wiring
and/or plug connection.
Check operation.
YES