American Standard UHMB060ACV3VB Series Service Facts page 44

Service Facts
DEFINITION:
Limit switches are safety
devices that will open
when an abnormal high
temperature has been
sensed.
REMOVE ALL JUMPER
User Interface
WIRING TO SWITCHES!
shows a
Under no circumstances,
HIGH LIMIT?
shall these switches be
left jumpered when not
troubleshooting.
Disconnect
electrical power to
furnace
Replace filter and
Are filter &
clean blower
NO blower wheel
wheel.
clean?
Check operation
YES
Check set screw
position and motor
Does blower
bearings. Correct
NO wheel turn
or replace as
freely?
needed.
Check operation
YES
Cycle power to
furnace and call
for heat
Ignition occurs and
FAN ON delay
begins
Does fan come
on after ~45
seconds?
YES
Is external
Correct application
static pressure
or duct issues. YES
greater than
Check operation
nameplate?
NO
Is heat rise
within
specification?
See Service
Facts
YES
Is outlet
Correct gas
manifold gas
pressure NO
pressure within
Check operation
specifications?
44
4 Flash Fault LED
Scroll through
User Interface to
View number 1 of
Last 4 Faults
See serial motor checkout in
Service Facts or on 10 Flash
Replace furnace control
LED section.
Replace if needed
YES
NO
Is 120 vac
measured at motor
NO
NO
(5 pin connector
terminals 4 and 5)?
Return air
temperature is
above max limit.
YES
Check for loose
Is return air
insulation or other
NO temperature NO
above 85 F?
furnace air stream
YES
Is temperature at
high limit above
YES
the switch setting?
See NOTE
NO
Replace high limit
switch
electrical power to
Check set screw
position and motor
bearings. Correct
NO
or replace as
needed.
Check operation
Ignition occurs and
Check operation
NO
NO
Is 120 vac
measured at 9
pin motor
harness
connector?
YES
Replace wiring
harness.
Check operation
Is temperature at auxilary
specifications after heat
fan off delay ends?
objects within
Check for excessive
reverse flow during an off
NOTE: Make sure any
temperature measuring
devices (thermocouples, dial
thermometers) used to
estimate limit temperature
are within ¼ inch of limit
measurement point
See next page for
additional 4 flash
faults
User Interface
shows a
AUX LIMIT?
(reverse flow)
Disconnect
furnace
Does blower
wheel turn
freely?
YES
Cycle power to
furnace and call
for heat
FAN ON delay
begins
Does fan come
on after ~45
seconds?
YES
Does motor
continue to run
during the
entire heating
cycle?
YES
Replace auxiliary
limit switch above
NO
limit switch
YES
cycle
UHM-DHM-SF-1V-EN