521271-UIM-D-1211
Johnson Controls Unitary Products
23
ADJUSTMENT OF TEMPERATURE RISE
After about 5 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.
All direct-drive blowers have multi-speed motors. The blower motor
speed taps are located on the furnace control board in the blower com-
partment. Refer to Figure 26, and the unit-wiring label to change the
blower speed. To use the same speed tap for heating and cooling, the
heat terminal and cool terminal must be connected using a jumper wire
and connected to the desired motor lead.
ADJUSTMENT OF FAN CONTROL SETTINGS
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.
MANIFOLD PRESSURE “U” TUBE CONNECTION
FIGURE 25:
Reading Gas Pressure
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 SECTION 7.
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.
U-TUBE
MANOMETER
3.5 IN
WATER
COLUMN
GAS
PRESSURE
SHOWN
GAS
BURNERS
OUTLET
PRESSURE TAP
GAS VALVE
FLAME
SENSOR
1/4” TUBING
MAINIFOLD
PIPE
DANGER
Do not energize more than one motor speed at a time or damage to
the motor will result.
FIGURE 26:
Furnace Control Board
L
ELECTRONIC AIR
CLEANER TERMINA
HUMIDIFIER
TERMINAL
DIAGNOSTIC ERROR CODE
RETRIEVAL BUTTON
CONTINUOUS FAN
SPEED JUMPER
BLOWER OFF
DELAY JUMPER
