035-20464-002 Rev. A (1004)
Unitary Products Group
21
IMPORTANT:
The inlet gas pressure operating range table specifies
what the minimum and maximum gas line pressures must be for the fur-
nace to operate safely. The gas line pressure
MUST BE
•
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.
ADJUSTMENT OF MANIFOLD GAS PRESSURE
Manifold gas pressure may be measured by connecting the “U” tube
manometer to the gas valve with a piece of tubing and on an adapter.
Follow the appropriate section in the instructions below. Refer to Figure
26 for a drawing of 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 Pressure Tap and Inlet Pressure Tap.
1.
The manifold pressure must be taken at the port marked OUT
Pressure Tap.
2.
The gas line pressure must be taken at the port marked Inlet Pres-
sure Tap.
Using a screw driver, remove the cap that covers the manifold pressure
set screw.
Read the inlet gas pressure
Connect the positive side of the manometer to the adapter previously
installed in the Out pressure Tap on the gas valve. Do not connect any
tubing to the negative side of the manometer, as it will reference atmo-
spheric pressure. Refer to Figure 27 for connection details.
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.
NOTE:
The regulated outlet pressures, both low and high, have been
calibrated at the factory. Additional pressure adjustment should
not be necessary. If adjustment is necessary, set to the following
specifications. After adjustment, check for gas leakage.
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:
IMPORTANT:
If gas valve regulator is turned in (clockwise), manifold
pressure is increased. If screw is turned out (counterclockwise), mani-
fold pressure will decrease.
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” (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 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 14:
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.
TABLE 15:
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 28:
Gas Valve
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.
MAINFOLD PRESSURE “U” TUBE CONNECTION
FIGURE 29:
Reading Gas Pressure
INLET
WRENCH
BOSS
INLET
PRESSURE
PORT
ON
OFF
ON/OFF SWITCH
(Shown in ON position)
MAIN REGULATOR
ADJUSTMENT
OUTLET
OUTLET
PRESSURE
PORT
VENT PORT
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
