25
Gas Input Rate measurement (Natural Gas Only)
The gas input rate to the furnace must never be greater than
that specified on the unit rating plate. To measure natural
gas input using the gas meter, use the following procedure.
1. Turn OFF the gas supply to all other gas-burning
appliances except the furnace.
2. While the furnace is operating, time and record one
complete revolution of the smallest gas meter dial.
3. Calculate the number of seconds per cubic foot (sec/
ft
3
) of gas being delivered to the furnace. If the dial is
a one cubic foot dial, divide the number of seconds
recorded in step 2 by one. If the dial is a two cubic foot
dial, divide the number of seconds recorded in step 2
by two.
4. Calculate the furnace input in BTUs per hour (BTU/ hr).
Input equals the sum of the installation’s gas heating
value and a conversion factor (hours to seconds)
divided by the number of seconds per cubic foot. The
measured input must not be greater than the input
indicated on the unit rating plate.
EXAMPLE:
Installation’s gas heating (HTG) value: 1,000 BTU/ft
3
(Obtained from gas supplier)
Installation’s seconds per cubic foot: 34 sec/ ft
3
Conversion Factor (hours to seconds): 3600 sec/hr
Input = (Htg. value x 3600) ÷ seconds per cubic foot
Input = (1,000 BTU/ft
3
x 3600 sec/hr) ÷ 34 sec/ ft
3
Input = 106,000 BTU/hr
This measured input must not be greater than the input
indicated in Specification Sheet.
5. Turn ON gas and relight appliances turned off in step
1. Ensure all the appliances are functioning properly
and that all pilot burners are operating.
TEMPERATURE RISE
Air temperature rise is the temperature difference between
supply and return air. The proper amount of temperature
rise is usually obtained when the unit is operated at the
rated input with the “as shipped” blower speed. If the
correct amount of temperature rise is not obtained, it may
be necessary to change the blower speed.
An incorrect temperature rise can cause condensing in or
overheating of the heat exchanger. Determine and adjust
the temperature rise as follows. The temperature rise must
be within the range specified on the rating plate or Specifi-
cation sheet.
1. Operate furnace with burners firing approximately 15
minutes. Ensure all registers are open and all duct
dampers are in their final (fully or partially open) posi-
tion.
2. Place thermometers in the return and supply ducts as
close to the furnace as possible. Thermometers must
not be influenced by radiant heat by being able to “see”
the heat exchanger.
3. Subtract the return air temperature from the supply air
temperature to determine the air temperature rise.
Allow adequate time for thermometer readings to sta-
bilize.
4. Adjust temperature rise by adjusting the circulator
blower speed. Increase blower speed to reduce tem-
perature rise. Decrease blower speed to increase tem-
perature rise. Refer to the following section for speed
changing details.
CIRCULATOR BLOWER SPEEDS
WARNING
To avoid death or personal injury due to
electrical shock, turn off power to the
furnace before changing speed taps.
This furnace is equipped with a multi-speed circulator
blower. This blower provides ease in adjusting blower
speeds. The Specification Sheet provides an airflow table,
showing the relationship between airflow (CFM) and exter-
nal static pressure (E.S.P.), for the proper selection of
heating and cooling speeds. The cooling blower speed is
shipped set on HIGH, and the heating blower speed is set
as indicated in the Specifications Sheet. These blower
speeds should be adjusted by the installer to match the
installation requirements so as to provide the correct heat-
ing temperature rise and the correct cooling CFM.
To adjust the circulator blower speed, proceed as follows:
1. Turn OFF power to the furnace.
2. Select the heating and cooling blower speeds that
match the installation requirements from the airflow
table in the Specification Sheet.
3. Relocate desired motor leads to the circulator blower
heat and cool speed terminals on the integrated control
module. (Terminals are identified as HEAT and COOL
(hot)). If heating and cooling blower speeds are the
same, a jumper wire must be used between the heat
and cool terminals.
4. Connect all unused blower motor leads to the “PARK”
terminals on the integrated control module. Any leads
not connected to the “PARK” terminals must be taped.
5. Turn ON power to furnace.
6. Verify proper temperature rise as outlined in
Section
XIV, Startup, Adjustments,and Checks - Temperature
Rise
.
Orange
High
Common/Neutral
Medium Low
Circulator Blower Speeds
Low
Red
Medium Blue
Black
White
Wiring Designations
