5. A problem affecting the main
blower:
A. A wrong speed tap selection.
B. Failing motor bearings.
C. Low voltage to the motor.
D. Dirty blower wheel.
E. Wrong motor rotation.
F. Blower wheel slipping on the
motor shaft.
6. Overtiring the furnace with too
much gas pressure.
CO AND CO2 LEVELS
IN FLUE GASES
The carbon monoxide (CO) or carbon
dioxide (CO
2
)
indicate much about the
combustion process and operation of
the Low Profile Furnace. Use the
following procedure to sample the CO
and CO
2
levels in the flue gases.
1. Let the furnace operate for 1
Oto 12
minutes to warm to normal
operating temperature.
2. Drill as small a hole as necessary
in the vent pipe near the furnace.
Make the hole in an inconspicuous
location.
3. Make the tests with a CO and CO
2
tester. Follow the test equipment
manufacturer's pro-cedure to
sample the flue gas.
A. Low Profile Furnace CO%
Range: 0.0--40.0 PPM
B. Low Profile Furnace CO
2
%
Range: 6.8%-8.0%
4. After making the test, seal the
opening in the exhaust pipe. Use a
high temperature sealant to
prevent any flue gas escape.
Possible causes for high CO
2
levels:
A. Inadequate combustion air.
B. Poor exhaust pipe design or
sizing
C. Overtiring with too much gas
pressure
Possible causes for low CO
2
levels:
A. Too much combustion air.
B. Undertiring with too little gas
pressure.
NOTE: If the CO
2
level is within the
normal range, the CO level should also
be within its normal range.
NOTE: Sooting results from the same
causes as high CO and CO
2
.
FLUE GAS
TEMPERATURE
RANGE
The usual flue gas temperature
range is 320°-410°F. Make a hole in
the exhaust pipe using the same
procedure as when measuring the
CO and CO
2
percentage. Use a
thermometer to measure the flue gas
temperature.
Possible causes for high flue gas
temperature:
A. Unit overtired with too much gas
pressure.
B. Restricted air flow.
Possible causes for low flue gas
temperature:
A. Too much air from the indoor
blower.
B. Undertiring the unit with too little
gas pressure.
Seal the hole in the vent when
finished.
FIGURE 110
CHECKING FLUE TEMPERATURE
100
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