129098-UIM-G-0411
Johnson Controls Unitary Products
23
CHECKING THE GAS PRESSURES
1.
The pressure ports on the gas valve are marked OUT PRESSURE
TAP and INLET PRESSURE TAP.
2.
The manifold pressure must be taken at the port marked OUT P.
3.
The inlet gas supply pressure must be taken at the port marked IN
P.
4.
Using a 3/32” (0.2 cm) Allen wrench, loosen the set screw by turn-
ing it 1 turn counter clockwise. DO NOT REMOVE THE SET
SCREW FROM THE PRESSURE PORT.
5.
Push one end of the 3/8” (0.9 cm) ID flexible tubing over the pres-
sure port so that the body of the port is inside the tubing.
6.
Use a reducer connector to connect the 3/8” (0.9 cm) ID flexible
tube that is connected to a “U” tube manometer or digital pressure
measuring equipment.
The minimum inlet gas pressure required to obtain the BTU input speci-
fied on the rating plate and in these instructions is shown below:
•
4.5” W.C. (1.12 kPA) for Natural Gas
•
11.0” W.C. (2.74 kPA) for Propane (LP) Gas
ADJUSTMENT OF MANIFOLD GAS PRESSURE
Manifold gas pressure may be measured at 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.
The manifold pressure must be taken at the port marked OUT P.
2.
The gas line pressure must be taken at the port marked IN P.
3.
Using a 3/32” Allen wrench, loosen the set screw by turning it 1
turn counter clockwise. DO NOT REMOVE THE SET SCREW
FROM THE PRESSURE PORT.
Use the 4” (10.2 cm) piece of 1/8” (0.3 cm) tubing to connect the posi-
tive side of the manometer to the gas valve pressure reference port.
Refer to Figure 30 for connection details.
1.
Refer to Figure 29 for location of pressure regulator adjustment
cap and adjustment screw on main gas valve.
2.
Turn gas and electrical supplies on and follow the operating
instructions 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
furnace 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 and fittings from the gas valve pressure
tap and tighten the pressure tap plug using the 3/32” 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 gas detector, a non-corrosive
leak detection fluid, or other leak detection methods.
Be sure to relight any gas appliances that were turned off at the
start of this input check.
TABLE 7:
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” (3.24 kPa) W.C.
The inlet gas pressure operating range table specifies the minimum
and maximum gas line pressures required for safe furnace opera-
tion.
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.
TABLE 8:
Nominal Manifold Pressure
NOMINAL MANIFOLD PRESSURE
Natural Gas
3.5" w.c. (0.87 kPa)
Propane (LP) Gas
10.0" w.c. (2.488 kPa)
FIGURE 29:
Gas Valve
If gas valve regulator is turned in (clockwise), manifold pressure is
increased. If screw is turned out (counter clockwise), manifold pres-
sure will decrease.
The manifold pressure must be checked with the screw-off cap for
the gas valve pressure regulator in place. If not, the manifold pres-
sure setting could result in an over-fire condition. A high manifold
pressure will cause an over-fire condition, which could cause pre-
mature heat exchanger failure. If the manifold pressure is too low,
sooting and eventual clogging of the heat exchanger could occur.
Be sure that gas valve regulator cap is in place and burner box to
gas valve pressure reference hose is connected.
INLET
ON/OFF SWITCH
(shown in OFF position)
OUTLET
SUPPLY
PRESSURE
TAP
OUTLET (MANIFOLD)
PRESSURE TAP
ELECTRICAL
CONNECTIONS
MAIN REGULATOR
ADJUSTMENT
90°
FLANGE
