5402847-UIM-A-0917
Johnson Controls Unitary Products
25
2.
Once the correct gas inlet pressure has been established, see
Table 12, turn the gas valve to OFF and turn the electrical supply
switch to OFF; then remove the flexible tubing from the gas valve
pressure tap and tighten the pressure tap plug using the 3/32” (2.4
mm) Allen wrench.
3.
Turn the electrical and gas supplies back on, and with the burners
in operation, check for gas leakage around the gas valve pressure
port for leakage using an approved non-corrosive gas leak detec-
tion fluid, or other non-flammable leak detection methods.
Read the manifold gas pressure
Connect the positive side of the manometer to the adapter previously
installed in the OUT P Tap on the gas valve. Do not connect any tubing
to the negative side of the manometer, as it will reference atmospheric
pressure. Refer to Figure 29 for connection details.
1.
Refer to Figure 28 for location of pressure regulator adjustment cap
and adjustment screws on main gas valve.
2.
Turn gas and electrical supplies on and follow the operating instruc-
tions to place the unit back in operation.
3.
Adjust manifold pressure by adjusting gas valve regulator screw for
the appropriate gas per the following:
4.
After the manifold pressure has been adjusted, re-calculate the fur-
nace input to make sure you have not exceeded the specified input
on the rating plate. Refer to “CALCULATING THE FURNACE
INPUT (NATURAL GAS)”.
5.
Once the correct BTU (kW) input has been established, turn the
gas valve to OFF and turn the electrical supply switch to OFF; then
remove the flexible tubing from the gas valve pressure tap and
tighten the pressure tap plug using the 3/32” (2.4 mm) Allen
wrench.
6.
Turn the electrical and gas supplies back on, and with the burners
in operation, check for gas leakage around the gas valve pressure
port for leakage using an approved non-corrosive gas leak detec-
tion fluid, or other non-flammable leak detection methods.
IMPORTANT
The inlet gas pressure operating range table specifies what the mini-
mum and maximum gas line pressures must be for the furnace to
operate safely. The gas line pressure MUST BE a minimum of:
•
7” w.c. (1.74 kPA) for Natural Gas
•
11” w.c. (2.74 kPA) for Propane (LP) Gas
in order to obtain the BTU input specified on the rating plate and/or
the nominal manifold pressure specified in these instructions and on
the rating plate.
IMPORTANT
The cap for the pressure regulator must be removed entirely to gain
access to the adjustment screw. Loosening or tightening the cap does
not adjust the flow of gas.
NOTICE
The regulated outlet pressures, both low and high, have been cali-
brated at the factory. Additional pressure adjustment should not be
necessary. If adjustment is necessary, set to the following specifica-
tions. After adjustment, check for gas leakage.
NOTICE
This furnace uses a two stage gas valve. The high-fire and low-fire
manifold pressures can be adjusted independently.
Table 13:
Nominal Manifold Pressure
NOMINAL MANIFOLD PRESSURE
Natural Gas
High Fire
Low Fire
3.5" w.c. (0.87 kPa)
1.5" w.c. (0.37 kPa)
Propane (LP) Gas
10.0" w.c. (2.488 kPa)
4.2" w.c. (1.04 kPa)
FIGURE 28:
Gas Valve
IMPORTANT
If gas valve regulator is turned in (clockwise), manifold pressure is
increased. If screw is turned out (counter clockwise), manifold pres-
sure will decrease.
MANIFOLD PRESSURE “U” TUBE CONNECTION
FIGURE 29:
Reading Gas Pressure
INLET
WRENCH
BOSS
INLET
PRESSURE
PORT
ON OFF
SWITCH
LOW STAGE REGULATOR
ADJUSTMENT
OUTLET
OUTLET
PRESSURE
PORT
VENT
PORT
HIGH STAGE REGULATOR
ADJUSTMENT
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
