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SERVICE AND TECHNICAL SUPPORT MANUAL
Gas Furnace: N9MSB
Specifications subject to change without notice.
440 04 4413 03
7
Figure 3
Automatic Gas Valve (Single Stage)
without Tower Pressure Ports
ON/OFF Switch
Regulator Seal Cap
Regulator Adjustment
Regulator Seal Cap under Cap
1/2” NPT Outlet
1/8” NPT Manifold
Pressure Tap
1/8” NPT Inlet
Pressure Tap
1/2” NPT Inlet
A11153
Gas Valve (Single Stage) with Tower Pressure
Ports
ON/OFF SWITCH
1/8” NPT INLET
PRESSURE TAP
REGULATOR SEAL CAP
(REGULATOR ADJ.
UNDER CAP)
1/2” NPT
OUTLET
MANIFOLD PRESSURE TAP
SET SCREW: 3/32” HEX HEAD
ACCEPTS 5/16” HOSE CONNECTION
OUTP
INP
VENT
1/2” NPT
INLET
INLET PRESSURE
TAP SET SCREW:
3/32” HEX HEAD
ACCEPTS 5/16”
HOSE CONNECTION
Representative drawing only, some models may vary in appearance.
1/8” NPT
INLET PRESSURE TAP
1/2” NPT
INLET
1/2” NPT
OUTLET
Representative drawing only, some models may vary in appearance.
A170118
A170133
2. Verify natural gas input rate by clocking meter.
NOTE
: Contact your HVAC distributor or gas supplier for metric
gas meter Tables, if required.
a. Turn off all other gas appliances and pilots served by
the meter.
b. Jumper R to W.
c. Run furnace for 3 minutes.
d. Measure time (in sec) for gas meter to complete 1
revolution and note reading. The 2 or 5 cubic feet dial
provides a more accurate measurement of gas flow.
e. Refer to
for cubic ft. of gas per hr.
f. Multiply gas rate cu ft./hr by heating value (Btuh/cu
ft.) to obtain input. If clocked rate does not match
required input from Step 1, increase manifold
pressure to increase input or decrease manifold
pressure to decrease input. Repeat steps b through e
until correct input is achieved. Re
−
install regulator
seal cap on gas valve.
g. If clocked rate does not match required input from
Step 1, increase manifold pressure to increase input
or decrease manifold pressure to decrease input.
Repeat steps b through e of Step 1 until correct heat
input is achieved. Re--install regulator seal cap on
gas valve.
3. Restore furnace to normal operating condition.
a. Turn gas valve ON/OFF switch to OFF.
b. Remove water column manometer or similar device
from manifold pressure tap.
c. Tighten set screw on manifold tower pressure tap
with 3/32
−
in. hex wrench, or if 1/8
−
in. NPT plug was
removed, apply pipe dope sparingly to end of plug
and reinstall in the gas valve.
d. Turn gas valve ON/OFF switch to ON.
e. Check for gas leaks and verify furnace operation
FIRE HAZARD
Failure to follow this warning could result in personal injury,
death, and/or property damage.
Manifold pressure tap set screw must be tightened and
1/8
−
in. NPT pipe plug must be installed to prevent gas
leaks.
!
WARNING