48
3. Subtract the return air temperature from the supply
air temperature to determine the air temperature
rise. Allow adequate time for thermometer readings to
stabilize.
4. Adjust temperature rise by adjusting the circulator
blower speed. Increase blower speed to reduce
temperature rise. Decrease blower speed to increase
temperature rise. Refer to
Startup Procedure and
Adjustment -Circulator Blower Speeds
for speed
changing details.
SUPPLY
AIR
RETURN
AIR
Temperature Rise Measurement
Figure 40
Circulator Blower Speeds
This furnace is equipped with a multi-speed ECM motor. The
line voltage (115 VAC) power supply to the motor is constant
and not switched by the control board. Motor operation is
also dependent on a pulsing D.C. signal on one of the four
speed taps on the motor. The airflow tables for heating and
cooling speeds show the relationship between airflow (CFM)
and external static pressure for each size furnace.
T
O
AVOID
PERSONAL
INJURY
OR
DEATH
DUE
TO
ELECTRICAL
SHOCK
,
TURN
OFF
POWER
TO
THE
FURNACE
BEFORE
CHANGING
SPEED
TAPS
.
WARNING
Circulator Blower Speed Facts
1. Motor speed Tap wiring must remain in factory
position on the control board and motor.
2. There are 4 speed Tap wires to the motor T1, T2, T3,
T4.
3. There are 5 speeds available, depending on DIP
switch settings and found in air flow table for each
size furnace.
4. Heating input (W1/ W2) always has priority over all
other thermostat input.
5. Cooling input (YLo/ Y) has priority over continuous
fan input.
6. Continuous fan input (G) has lowest priority.
Gas Input Rate Measurement (Natural Gas Only)
The actual 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 at high fire rate, time
and record one complete revolution of the gas meter
dial measuring the smallest quantity, usually the dial
that indicates 1/2 cu. ft. per revolution. You will use
this number to calculate the quantity of gas in cubic
ft. if the furnace would consume if it ran steadily for
one hour (3600 seconds).
3. If the 1/2 cu. ft. dial was used, multiply your number
x 2.
EXAMPLE: If it took 23 seconds to complete one
revolution of the 1/2 ft. dial (23 x 2 = 46).
This tells us that at this rate, it would take 46 seconds to
consume one cu. ft. of gas. 3600 / 46 = 78.
This tells us that in one hour, the furnace would consume
78 cu. ft. of gas.
The typical value range for 1 cu. ft. of natural gas is around
1000 BTU. Check with your gas utility, if possible. In this
example, the furnace is consuming 78,000 BTUH.
NOTE:
The final manifold pressure cannot vary by
more than ± 0.3” w.c. for Natural and + 0.5” for
LP from the specified setting. Consult your local
gas supplier if additional input rate adjustment is
required.
4. Turn ON gas to and relight all other appliances turned off
in step 1. Be certain that all appliances are functioning
properly and that all pilot burners are operating.
Temperature Rise
Temperature rise must be within the range specified on the
unit rating plate. An incorrect temperature rise may result in
condensing in or overheating of the heat exchanger. An airflow
and temperature rise table is provided in the Specification Sheet
applicable to your model. Determine and adjust temperature
rise as follows:
1. Operate furnace with burners firing for approximately
ten minutes. Ensure all registers are open and all
duct dampers are in their final (fully or partially open)
position.
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.
