5285473-UIM-E-1217
Johnson Controls Unitary Products
19
ADJUSTMENT OF MANIFOLD GAS PRESSURE &
INPUT RATE
Inlet and manifold gas pressure may be measured by connecting the
“U” tube manometer to the gas valve with a piece of tubing. Follow the
appropriate section in the instructions below. Refer to Figure 10 for the
locations of the pressure ports on the gas valve.
Turn gas off at the ball valve or gas cock on gas supply line
before the gas valve. Find the pressure ports on the gas
valve marked Out P and In P.
1.
Take the manifold pressure at the port marked OUT P.
2.
Take the gas line pressure at the port marked IN P.
3.
Using a 3/32” (2.4 mm) hex head wrench, loosen the set screw by
turning it 1 turn counter clockwise. DO NOT REMOVE THE SET
SCREW FROM THE PRESSURE PORT.
Read the inlet gas pressure
Connect the positive side of the manometer to the port marked IN P on
the gas valve. Do not connect any tubing to the negative side of the
manometer to prevent atmospheric pressure from being referenced by
the manometer. Refer to Figure 11 for connection details.
1.
Turn gas and electrical supplies on and follow the operating instruc-
tions to place the unit back in operation.
2.
Establish the correct gas inlet pressure in accordance with Table
15. Turn the gas valve to OFF, and turn the electrical supply switch
to OFF. Then remove the flexible tubing from the gas valve pres-
sure port, and tighten the pressure port plug using the 3/32” (2.4
mm) hex head wrench.
3.
Turn the electrical and gas supplies back on. With the burners in
operation, check for gas leakage around the gas valve pressure
port. Use an approved non-corrosive gas leak detection fluid or
other non-flammable leak detection methods to accomplish the leak
check.
Read the manifold gas pressure
Connect the positive side of the manometer to the port marked OUT P
on the gas valve. Do not connect any tubing to the negative side of the
manometer to prevent atmospheric pressure from being referenced by
the manometer. Refer to Figures 10 and 11 for connection details.
This gas valve has separate regulator adjustment screws for high fire
and low fire as shown in Figure 10. The procedure below is used to
adjust either the high fire manifold pressure or the low fire manifold
pressure.
1.
Refer to Figure 10 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
instructions to place the unit back in operation.
3.
Connect unit control wiring leads W1, W2, and R together so the
equipment operates on HIGH fire. Once correct manifold pressure
is set (HI), remove control wire lead W2 so the equipment operates
on low fire. Set the manifold pressure (LO) to correct manifold pres-
sure.
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)”.
Table 15:
Inlet Gas Pressure Range
INLET GAS PRESSURE RANGE
Natural Gas
Propane (LP)
Minimum
4.5” w.c. (1.12 kPa)
8.0” w.c. (1.99 kPa)
Maximum
10.5” w.c. (2.61 kPa)
13.0” w.c. (3.24 kPa)
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 pressure has been calibrated at the factory.
Additional pressure adjustment should not be necessary. If adjust-
ment is necessary, set to the following specifications. After adjust-
ment, check for gas leakage.
NOTICE
Gas manifold pressure must be set on high fire before adjusting low
fire pressure.
Table 16:
Nominal Manifold Pressure
NOMINAL MANIFOLD PRESSURE
Natural Gas (High Fire)
3.5" w.c. (0.87 kPa)
Natural Gas (Low Fire)
1.6" w.c. (0.40 kPa)
Propane (LP) Gas (High Fire)
9.8" w.c. (2.488 kPa)
Propane (LP) Gas (Low Fire)
4.0" w.c. (0.99 kPa)
FIGURE 10:
Gas Valve
IMPORTANT
If gas valve regulator screw is turned in (clockwise), manifold pres-
sure is increased. If screw is turned out (counterclockwise), manifold
pressure is decreased.
287/(7
35(6685(
3257
+,*+67$*(5(*8/$725
$'-8670(17
9(17
3257
287/(7
/2:67$*(5(*8/$725
$'-8670(17
212))
6:,7&+
,1/(7
35(6685(
3257
:5(1&+
%266
,1/(7
$
