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the blower speed. Lowering the blower speed increases
the temperature rise and a higher speed decreases the
temperature rise.
The unit is equipped with a variable speed motor. Heating
and cooling speed selection is made by changing the dip
switch settings on the blower control board located in the
unit control box. Refer to Configuring the Variable Speed
Blower Section (page 13) for additional information.
NOTE: For change in blower speed selection to take
effect, system power must be cycled off then restored
after 10 seconds.
The Variable Speed Blower (VSB) Control Board (Figure
13, page 30) is designed with built in delay profiles for start
up and shut down of the system. Refer to the Operating
Sequence section (pages 19-20) for more details.
Verifying & Adjusting Firing Rate
CAUTION:
Do not re-drill the burner orifices. If the orifice
size must be changed, use only new orifices.
The firing rate must be verified for each installation to
prevent over-firing of the furnace. The firing rate must
not exceed the rate shown on the unit data label. To
determine the firing rate, follow the steps below:
1. Obtain the gas heating value (HHV) from the gas supplier.
2. Shut off all other gas fired appliances.
3. Start the unit in heating mode and allow it to run for at
least 3 minutes.
4. Measure the time (in seconds) required for the gas
meter to complete one revolution.
5. Convert the time per revolution to cubic feet of gas per
hour using Table 16 (page 28).
6. Multiply the gas flow rate in cubic feet per hour by the
heating value of the gas in Btu per cubic foot to obtain
the firing rate in Btu per hour. See Example.
Example:
• Time for 1 revolution of a gas meter with a 1 cubic
foot dial = 40 seconds.
• From Table 16, read 90 cubic feet gas per hour.
• Local heating value of the gas (obtained from gas
supplier) = 1,040 Btu per cubic foot.
• Input rate = 1,040 x 90 = 93,600 Btuh.
7. Adjust the manifold pressure if necessary. See Manifold
Pressure Adjustment instructions. For additional
information about elevations above 2,000 feet, see
page 15.
18
Verifying Over-Temperature Limit Control
Operation
1. Verify the louvered control access panel is in place and
that there is power to the unit.
2. Block the return airflow to the unit by installing a close-
off plate in place of or upstream of the filter.
3. Set the thermostat above room temperature and verify
the units operating sequence (pages 19-20).
NOTE: The over-temperature limit control should turn
off the gas valve within approximately four minutes
(exact time depends on the efficiency of the close-off
when blocking the return air). The circulating air and
combustion blowers should continue to run when the
over-temperature limit control switch opens.
4. Remove the close-off plate immediately after the over-
temperature limit control opens. If the unit operates
for more than four minutes with no return air, set the
thermostat below room temperature, shut off power to
the unit, and replace the over-temperature limit control.
Verifying Burner Operation
WARNING:
Uninsulated live components are exposed when
louvered control access panel is removed.
1. Remove the louvered control access panel and verify
there is power to the unit.
2. Set thermostat above room temperature and observe
the ignition sequence. NOTE: The burner flame should
carry over immediately between all burners without
lifting off, curling, or floating. The flames should be blue,
without yellow tips. Make sure the flame is drawn into
the center of the heat exchanger tube. In a properly
adjusted burner assembly, the flame bends down and
to the right at the end of the heat exchanger tube. The
end of the flame will be out of sight around the bend.
3. After validating flame characteristics, set the thermostat
below room temperature and verify the burner flame
extinguishes completely.
Manifold Pressure Adjustment
The manifold pressure must be set to the appropriate
value for your installation.To adjust the manifold pressure:
1. Obtain the required manifold pressure setting. Use Table
5 for natural gas or Table 6 (page 16) for LP/propane
gas. NOTE: The values listed in the tables are based
on sea level values. At higher altitudes, the heating
value of gas is lower than the sea level heating value.
2. Remove the regulator cap. Turn the high fire
adjusting screw clockwise to increase the pressure or
counterclockwise to reduce the pressure. See Figure
9 (page 23) for adjusting screw locations.
3. Replace the regulator cap after adjustments are
complete.
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