21
Verifying & Adjusting Input Rate
The input rate must be verified for each installation to
prevent over-firing of the furnace.
NOTE:
The input rate
must not exceed the rate shown on the furnace rating plate.
To determine the exact input rate, perform the following
procedures:
1. Shut off all other gas fired appliances.
2. Start the furnace and run it for at least 3 minutes.
3. Measure the time (in seconds) required for the gas meter
to complete one revolution.
4. Convert the time per revolution to cubic feet of gas per
.
5. Multiply the gas flow rate in cubic ft per hr by the heating
value of the gas in Btu per cubic ft to obtain the input rate
in Btuh. See example.
EXAMPLE:
• Time for 1 revolution of a gas meter with a 1 cubic ft
dial = 40 seconds.
• From
read 90 cubic ft gas per hr.
• Local heating value of the gas (obtained from gas
supplier) = 1,040 Btu per cubic ft.
• Input rate = 1,040 x 90 = 93,600 Btuh.
6. The manifold pressure must be set to the appropriate
value for each installation by a qualified installer, service
agency or the gas supplier.
WARNING:
Do not attempt to drill the gas orifice. Use only
the factory supplied orifice. Improperly drilled
orifices may cause fire, explosion, carbon
monoxide poisoning, personal injury or death.
a.) Obtain the manifold pressure setting required for this
b.) Remove the regulator capscrew (
) from the
INLET side of the regulator.
c.) Slowly turn the adjustment screw inside the regulator
to obtain the appropriate manifold pressure.
NOTE:
Turning the screw clockwise increases the
pressure and turning the screw counter-clockwise
decreases the pressure. To prevent backing the screw
all the way out from the valve, turn the screw slowly.
d.) Replace and tighten the regulator capscrew over the
adjustment screw.
Verifying & Adjusting Temperature Rise
After installation of the furnace, confirm the temperature rise
of the furnace is within the limits specified on the rating plate.
Any temperature rise outside the specified limits could result
in premature failure of the heat exchanger.
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 specified on the rating plate with the blower speed at the
factory recommended setting. If the measured temperature
rise is outside the specified 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
and cooling speed selection is made by selections on the
menu and option buttons on the control board. The LED
shows which options are selected.
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 and note the location
of the sightglass on burner head.
2. Set the thermostat above room temperature and observe
the ignition sequence.
NOTE:
The burner flame should be
present by seeing a glow through the sightglass.
3. After validating the flame, change the thermostat setting
to below room temperature.
4. Verify the burner flame is completely extinguished.
5. Replace the burner compartment door.
Verifying 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 airflow to the furnace by installing a close-
off plate in place of or upstream of the filter(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
power to the furnace, and replace the limit switch.
Figure 21. Regulator Capscrew
Capscrew
