21
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 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 will increase 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
switch on the integrated control located in 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.
NOTE:
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 the fl ame, change the thermostat
setting to below room temperature.
4. Verify the burner fl ame is completely extinguished.
5. Replace the burner compartment door.
Verify Operation of the Supply Air Limit Switch
Note:
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. Verify the blower door is securely mounted in place
and that there is power to the furnace.
2. Block the return airfl ow to the furnace by install-
ing 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 re-
turn 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 13, page 18), (Figure 14, page
19) and (Figure 18, page 31).
Heating Cycle
1. The thermostat calls for heat by energizing the
W
terminal with 24VAC.
2. The control verifi es the pressure switch is open.
3. If the pressure switch is open, the control energizes
the inducer and waits for the pressure switch to close.
The pressure switch must close within 10 seconds.
4. The control runs the inducer for a 30 second pre-
purge.
5. The control energizes the igniter output for the
appropriate warm-up time limit.
6. The control energizes the main gas valve for 3
seconds.
7. If the fl ame 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. If fl ame is present, 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. When the thermostat demand for heat is satisfi ed, the
control de-energizes the gas valve. The inducer output
remains on for a 30 second post-purge period.
10. Blower off timing begins when the thermostat is
satisfi ed. The control will operate at the selected HEAT
speed of 60, 90, 120, or 180 seconds. If the blower
off delay jumper is not present, the fan should still
operate for 120 seconds at the selected HEAT speed.
The Indoor blower motor is de-energized after a blower
off delay as selected by the movable jumper.
