129098-UIM-G-0411
24
Johnson Controls Unitary Products
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.
ADJUSTMENT OF FAN CONTROL SETTINGS
This furnace is equipped with a time-on/time-off heating fan control. The
fan off delay has 4 settings (60, 90, 120 and 180 seconds). The fan off
delay is factory set to 120 seconds. 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 31.
FILTER PERFORMANCE
The airflow capacity data published in Table 9 represents blower perfor-
mance WITHOUT filters.
APPLYING FILTER PRESSURE DROP TO
DETERMINE SYSTEM AIRFLOW
Example: For a 90,000 BTUH (26.4 kW) furnace operating on high-
speed blower, it is found that total system static is 0.18” (0.045 kPa) w.c.
To determine the system airflow, complete the following steps:
Obtain the airflow values at 0.10 w.c. (0.02 Pa) & 0.20 w.c. (0.05 Pa)
ESP.
Airflow @ 0.10”: 1425 CFM (40.4 m
3
/min)
Airflow @ 0.20”: 1380 CFM (38.2 m
3
/min)
Subtract the airflow @ 0.10 w.c. (0.02 Pa) from the airflow @ 0.20 w.c.
(0.05 Pa) to obtain airflow difference.
1425 - 1250 = -175 CFM (5.0 m
3
/min)
Subtract the total system static from 0.10 w.c. (125 Pa) and divide this
difference by the difference in ESP values in the table
0.18 w.c. (0.045 kPa) - 0.10 w.c. (125 Pa), to obtain a percentage.
(0.18 - 0.10) / (0.20 - 0.10) = 0.2
Multiply percentage by airflow difference to obtain airflow reduction.
(0.2) X (175) = -35 CFM (0.99 m
3
/min)
Subtract airflow reduction value to airflow @ 0.10 w.c. (125 Pa) to
obtain actual airflow @ 0.18 in. w.c. (0.045 kPa) ESP.
1425 (40.4) - 35 = 1390 (39.4 m
3
/min)
FINAL PROCEDURE
Install Furnace Doors
Install the lower door first by sliding the bottom of the door down until
the tabs on the casing base engage the slots in the bottom door end
cap. Then push the top of the lower door in until the door clips snap into
place. Install the upper door in a similar manner, first engaging the slots
in the top of the upper door on the tabs on the casing top. Then snap
the bottom of the upper door into place against the casing.
Finish and Trim
Alcove and Closet Installations may now be finished and trimmed as
necessary.
MANIFOLD PRESSURE “U” TUBE CONNECTION
FIGURE 30:
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 Table 7 “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.
Do not energize more than one motor speed at a time or damage to
the motor will result.
3.5 IN (0.87 kPa)
WATER
COLUMN
GAS
PRESSURE
SHOWN
GAS VALVE
TUBING
FIGURE 31:
Furnace Control Board
FAN ON
ADJUSTMENT
JUMPER
HEA
T
XFMR
L1
COOL
TRANSFORMER
LINE VOLTAGE
BLACK - HIGH SPEED
RED -LOW SPEED
FAN OFF
JUMPER
NEUTRALS
FUSE 3A