035-20499-001 Rev. B (1004)
20
Unitary Products Group
ADJUSTMENT OF TEMPERATURE RISE
The temperature rise, or temperature difference between the return air
and the heated supply air from the furnace, must be within the range
shown on the furnace rating plate and within the application limitations
as shown in Table 7.
After about 20 minutes of operation, determine the furnace temperature
rise. Take readings of both the return air and the heated air in the ducts,
about six feet (1.83 m) from the furnace where they will not be affected
by radiant heat. Increase the blower speed to decrease the temperature
rise; decrease the blower speed to increase the rise.
VARIABLE SPEED MOTORS
The variable speed motor CFM / Timer Control Board must be config-
ured so the blower will provide a sufficient airflow so that the furnace
operates with in the temperature rise range on the rating plate and
within the application limitations shown in Table 7 in these Instructions.
ADJUSTMENT OF FAN CONTROL SETTINGS
Heating Indoor Fan Off Delay
This furnace is equipped with a time-on/time-off heating fan control. The
fan on delay is fixed at 30 seconds. The fan off delay has 4 settings (60,
90, 120 and 180 seconds). The fan off delay is factory set to 120 sec-
onds. The fan-off setting must be long enough to adequately cool the
furnace, but not so long that cold air is blown into the heated space. The
fan-off timing may be adjusted by positioning the jumper on two of the
four pins as shown in Figure 26.
Heating and Cooling Airflow
The heating and the cooling airflows are preset at the factory. The heat-
ing airflow is set to the maximum CFM. The cooling airflow is set to pro-
vide 90 percent of the maximum CFM. The heating and cooling airflows
must be field adjusted to match the HVAC system at installation. See
Table 15 for the HEAT, COOL and ADJ jumper settings to use for spe-
cific airflows.
WITH BURNER BOX COVER IN PLACE
WITH BURNER BOX COVER REMOVED
FIGURE 25:
Reading Gas Pressure
6
5
4
3
2
1
0
1
2
3
4
5
6
BURNER BOX
WITH COVER
OUTLET
PRESSURE
TAP
GAS VALVE
U-TUBE
MANOMETER
TEE
FITTING
BURNER BOX
PRESSURE
REFERENCE
HOSE
3.5 IN
WATER
COLUMN
GAS PRESSURE
SHOWN
6
5
4
3
2
1
0
1
2
3
4
5
6
U-TUBE
MANOMETER
3.5 IN
WATER
COLUMN
GAS PRESSURE
SHOWN
BURNER BOX
WITH COVER
REMOVED
OUTLET
PRESSURE
TAP
GAS VALVE
BURNER BOX
PRESSURE
REFERENCE
HOSE
(not used)
The temperature rise, or temperature difference between the return
air and the supply (heated) air from the furnace, must be within the
range shown on the furnace rating plate and within the application
limitations shown in Table 8 “ELECTRICAL AND PERFORMANCE
DATA”.
The supply air temperature cannot exceed the “Maximum Supply
Air Temperature” specified in these instructions and on the fur-
nace rating plate. Under NO circumstances can the furnace be
allowed to operate above the Maximum Supply Air Temperature.
Operating the furnace above the Maximum Supply Air Temperature
will cause premature heat exchanger failure, high levels of Carbon
Monoxide, a fire hazard, personal injury, property damage, and/or
death.
FIGURE 26:
Furnace Control Board
Y1
Y2
Y
W1
W
W2
R
G
C
BLOWER OFF
DELAY JUMPER
W2 DELAY
JUMPER
CONTINUOUS
FAN SPEED
JUMPER
