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NOTE: Turning the adjusting screw clockwise
increases the pressure and counterclockwise
reduces the pressure.
d.) Reinstall plastic cap after adjustment is complete.
Verifying & Adjusting Temperature Rise
Confi rm the temperature rise through the furnace is
within the limits specifi ed on the furnace rating plate. Any
temperature rise outside the specifi ed limits could result
in premature failure of the heat exchanger.
WARNING:
To prevent electric shock, personal injury, or
death, disconnect the electric power before
performing any maintenance.
1. Place thermometers in the return and supply air stream
as close to the furnace as possible. The thermometer on
the supply air side must be shielded from direct radiation
from the heat exchanger to avoid false readings.
2. Adjust all registers and duct dampers to the desired
position and run the furnace in high fi re for 10 to 15
minutes before taking any temperature readings. The
temperature rise is the difference between the supply
and return air temperatures.
For typical duct systems, the temperature rise will fall
within the limits specifi ed on the rating plate with the
blower speed at the factory recommended setting. If
the measured temperature rise is outside the specifi ed
limits, it may be necessary to change the speed of the
blower. NOTE: Lowering the blower speed increases the
temperature rise and a higher blower speed will decrease
the temperature rise.
The furnace is equipped with a multi-speed motor. Heating,
cooling, and fan speed selection is made by moving the
switches on the integrated control inside the furnace.
Verifying Burner Operation
CAUTION:
The door over the burners may only be open
for inspection purposes only. The door must be
installed during unattended operation.
1. Remove the burner compartment door.
2. Set the thermostat above room temperature and observe
the ignition sequence. The burner fl ame should carry
over immediately between all burners without lifting off,
curling, or fl oating. The fl ames should be blue, without
yellow tips.
3. After validating fl ame characteristics, change thermostat
setting to below room temperature.
4. Verify burner fl ame is completely extinguished.
5. Replace the burner compartment door.
Verifying Operation of the Supply Air Limit
Switch
A properly functioning limit switch should turn off the
gas valve when the return is blocked (time depends on
how well the return air is blocked). The circulating air and
combustion blowers should continue to run when the limit
switch opens.
1. Check the blower door for secure mounting and that
there is power to the furnace.
2. Block the return airfl ow to the furnace by installing a
close-off plate in place of or upstream of the fi lter(s).
3. Set the thermostat above room temperature and observe
the Operating Sequence.
4. Remove the close-off immediately after the limit switch
opens. If the furnace continues to operate with no return
air, set the thermostat below room temperature, shut off
the power to the furnace, and replace the limit switch.
OPERATING SEQUENCE
The operating sequences for the heating, cooling, and fan
modes are described below. Refer to the fi eld and furnace
wiring diagrams: (Figure 14, page 19) , (Figures 15 - 17,
page 22), & (Figures 24 - 27, pages 34 - 37).
Heating Cycle
1. The thermostat calls for heat by energizing the W1
terminal with 24VAC.
2. The control checks to see the pressure switch is open.
If the switch is closed, the furnace will shut down for 5
minutes before retrying
3. If the pressure switch is open, the control energizes the
inducer motor and waits for the pressure switch to close.
The pressure switch must close within 12 seconds.
4. The control runs the inducer for a 30 second pre-purge
time.
5. The control energizes the igniter output for the
appropriate adaptive warm-up time limit.
6. The furnace always ignites the burners in high fi re. If
the call for heat is for low rate, the furnace will move
down to low fi re after the fl ames stabilize.
7. If the fl ame is proved and ignites the gas, the control
de-energizes the igniter. The gas valve and inducer
remains energized. The control goes to blower on delay.
8. The control energizes the blower on the selected HEAT
speed 30 seconds after the gas valve opened. The gas
valve and inducer remain energized.
9. If there is a call for high fi re, the gas valve moves to the
high fi re position and the blower speeds are increased.
The furnace will remain in high fi re until the demand
for heat is satisfi ed.
10. If autostaging is enabled (single stage thermostat) the
demand for heat has lasted more than the selected
time, the furnace automatically moves up to high fi re.
23
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