Reading Gas Pressure; Furnace Control Board - Johnson Controls TM9T Series Installation Manual

MANIFOLD PRESSURE "U" TUBE CONNECTION
OUTLET
PRESSURE TAP
GAS VALVE
FLAME
SENSOR
GAS
BURNERS
FIGURE 36: Reading Gas Pressure
ADJUSTMENT OF TEMPERATURE RISE
DANGER
!
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 6.
The supply air temperature cannot exceed the "Maximum Supply
Air Temperature" specified in these instructions and on the furnace
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 pre-
mature heat exchanger failure, high levels of Carbon Monoxide, a fire
hazard, personal injury, property damage, and/or death.
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.
DIAGNOSTIC ERROR CODE
RETRIEVAL BUTTON
FIGURE 37: Furnace Control Board
Johnson Controls Ducted Systems
1/4" TUBING
MAINIFOLD
PIPE
3.5 IN
WATER
COLUMN
GAS
PRESSURE
U-TUBE
SHOWN
MANOMETER
BLOWER OFF
DELAY JUMPER
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 37, 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. Place all unused motor leads
on Park terminals. One park terminal is provided.
CAUTION
!
Do not energize more than one motor speed at a time or damage to
the motor will result.
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 37.
TAKING A FLUE GAS SAMPLE
If it becomes necessary to obtain a flue gas sample for analysis, it is
permissible to drill a small hole in the plastic flue pipe for a sample
probe, provided that the vent piping is PVC and the hole is properly
sealed afterwards. If using a polypropylene vent system, the vent sys-
tems manufacturer test port fitting must be used. DONOT drill a test
port hole in polypropylene piping. Use the following procedure:
1. Drill a 11/32" hole in the side wall of the PVC vent pipe. If the hole is
in a horizontal section of the vent pipe, ensure that it is located
away from the bottom where condensation may be flowing back
toward the furnace.
2. Operate the furnace a minimum of (10 minutes) to ensure stable
operation of the combustion process.
3. Sample the flue gas as necessary to obtain CO readings.
4. Using a 1/8" pipe tap, cut threads into the sampling hole of the PVC
pipe.
5. Use high temp RTV as a sealant on the threads of a 1/8" brass
MPT plug and insert it 3 turns into the hole to correctly seal it.
CONTINUOUS FAN
SPEED JUMPER
1083286-UIM-L-1219
HUMIDIFIER
TERMINAL
ELECTRONIC AIR
L
CLEANER TERMINA
33