Trane S8B1A040M3PSC Installation, Operation And Maintenance Manual page 68

T T r r o o u u b b l l e e s s h h o o o o t t i i n n g g
DEFINITION
Limit switches are safety devices
that will open when an abnormal
high temperature has been sensed.
REMOVE ALL JUMPER WIRING TO
SWITCHES!
Under no circumstances, shall these
switches be le jumpered when not
troubleshoo ng.
Verify filters and blower wheels are
clean
Is 24 VAC
measured across
main thermal
limit?
YES
Is external sta c
YES pressure greater
than nameplate?
Correct applica on or
NO
duct issues.
Check opera on
Is heat rise
within
specifica on?
See Nameplate
YES
Is outlet
manifold gas
NO
pressure within
specifica ons?
Correct gas pressure
Check opera on
68
4.0 Fault Code
Is blower motor
running?
Are either of the
flame roll-out
switches tripped?
NO
Return air
temperature is
above max limit
YES
Is return air
NO temperature NO
above 80F?
YES
Is temperature at
YES high limit above the
switch se ng?
NO
Replace high limit
switch
YES
NO
NO
Check for loose
insula on or other
objects within
furnace air stream
Make sure any temperature
measuring devices
(thermocouples, dial
thermometers) used to
es mate limit temperature are
within ¼ inch of limit disc
See next page for
addi onal 4 flash
faults
See troubleshoo ng for
motor
Note:
S8X2 will need to be checked in both
st nd
1 & 2 stage opera on.
Reverse
Does motor
con nue to run
during the en re
hea ng cycle?
YES
Is temperature at
reverse flow switch
above
specifica ons?
YES Replace reverse flow
switch
Increase blower off delay
S8XB-SVX001-1B-EN
NO