035-19670-003 Rev. A (1004)
Unitary Products Group
19
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
29 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 30 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.
.
High Outlet Pressure Adjustment
1.
Turn off all electrical power to the system at main fuse or circuit
breaker.
2.
Attach a manometer to the outlet pressure tap of the valve.
3.
Turn on power and energize main and redundant (P.M.) solenoids
as well as the HI terminal.
4.
Remove high adjustment seal screw to expose the 3/32”. See Fig-
ure 29.
5.
To increase outlet pressure, turn the 3/32” set screw clockwise. To
decrease outlet pressure, turn the set screw counterclockwise.
Adjust regulator until pressure shown on manometer matches the
pressure specified on the appliance rating plate.
6.
Replace low adjustment seal screw and tighten securely. Cycle the
valve several times to verify regulator setting.
7.
Remove manometer and replace the outlet pressure tap plug.
Low Outlet Pressure Adjustment
1.
Turn off all electrical power to the system at main fuse or circuit
breaker.
2.
Attach a manometer to the outlet pressure tap of the valve.
3.
Turn on power and energize main and redundant (P.M.) solenoids.
Do not energize HI terminal.
4.
Remove low adjustment seal screw. See Figure 29.
5.
To increase outlet pressure, turn the 3/32” (0.24 cm) set screw
below the low adjustment seal screw clockwise. To decrease outlet
pressure, turn the set screw counterclockwise. Adjust regulator
until pressure shown on manometer matches the pressure speci-
fied on the appliance rating plate.
6.
Replace high adjustment seal screw and tighten securely. Cycle
the valve two and three times to verify regulator setting.
7.
Remove manometer and replace the outlet pressure tap.
IMPORTANT:
If gas valve regulator is turned in (clockwise), manifold
pressure is increased. If screw is turned out (counterclockwise), mani-
fold pressure will decrease.
8.
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)”.
9.
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 re-install the plug in the Out Pressure Port using a com-
pound (on the threads) resistant to the action of LP gases.
Replace the burner box front cover (if it was removed) and replace
the pressure reference hose.
10. 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.
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 (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)
10.0" w.c. (2.488 kPa)
Propane (LP) Gas (Low Fire)
4.0" w.c. (0.99 kPa)
FIGURE 27:
Gas Valve
R
E
P
L
A
C
E
R
E
P
L
A
C
E
SCRE
W
SCRE
W
INLET
OUTLET
ON / OFF SWITCH
WRENCH
BOSS
LOW FIRE
REGULATOR
ADJUSTMENT
SEAL SCREW
HIGH FIRE
REGULATOR
ADJUSTMENT
SEAL SCREW
HI ADJUST
LO
ADJUST
PM
C
HI
O
F
F
ON
