65
2. Obtain average yearly gas specific gravity from local gas
supplier.
3. Find installation altitude in Table 21.
4. Find closest natural gas heat value and specific gravity in
Table 21. Follow heat value and specific gravity lines to
point of intersection to find orifice size and manifold
pressure settings for proper operation.
5. Check and verify burner orifice size in furnace. NEVER
ASSUME ORIFICE SIZE. ALWAYS CHECK AND
VERIFY.
If orifice hole appears damaged or it is suspected to have been
redrilled, check orifice hole with a numbered drill bit of
correct size. Never redrill an orifice. A burr--free and squarely
aligned orifice hole is essential for proper flame characteristics.
NOTICE
6. Replace orifice with correct size, if required by Table 21.
Use only factory--supplied orifices. See EXAMPLE 1.
EXAMPLE
1: 0 -- 2000 ft. (0 -- 609.6M) altitude
Heating value = 1050 Btu/cu ft.
Specific gravity = 0.62
Therefore: Orifice No. 44
Manifold pressure: 3.4--in. w.c. (847 Pa)
(Furnace is shipped with No. 44 orifices. In this example, all main
burner orifices are the correct size and do not need to be changed to
obtain proper input rate.)
NOTE
: To convert gas manifold Table pressures to Pascals,
multiply the in. w.c. value by 249.1 Pa/in. w.c. (1 in. w.c. = 249.1
Pa).
Check Inlet Gas Pressure
The inlet gas pressure must be checked with the furnace operating
in maximum heat. This is necessary to make sure the inlet gas
pressure does not fall below the minimum pressure of 4.5 in. w.c.
1. Make sure the gas supply is turned off to the furnace and at
the electric switch on the gas valve.
2. Loosen set screw on inlet tower pressure tap no more than
one full turn with a 3/32--in. hex wrench or remove the
1/8--in. NPT plug from the inlet pressure tap on the gas
valve.
3. Connect a manometer to the inlet pressure tap on gas valve.
4. Turn on furnace power supply.
5. Turn gas supply manual shutoff valve to ON position.
6. Turn furnace gas valve switch to ON position.
7. Jumper R and W thermostat connections at the furnace
control board.
8. When main burners ignite, confirm inlet gas pressure is
between 4.5 in. w.c. (1125 Pa) and 13.6 in. w.c. (3388 Pa).
9. Remove jumper across thermostat connections to terminate
call for heat. Wait until the blower off delay is completed.
10. Turn furnace gas valve electric switch to OFF position.
11. Turn gas supply manual shutoff valve to OFF position.
12. Turn off furnace power supply.
13. Remove manometer from the inlet pressure tap of the gas
valve.
FIRE HAZARD
Failure to follow this warning could result in personal injury,
death, and/or property damage.
Inlet pressure tap set screw must be tightened and 1/8--in. NPT
pipe plug must be installed to prevent gas leaks.
!
WARNING
14. Tighten set screw on inlet 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 re--install in the gas
valve.
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
SINGLE-STAGE
Representative drawing only, some models may vary in appearance.
A11153
Fig. 61 -- Gas Valve without 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.
A170118
Fig. 62 -- Gas Valve with Tower Pressure Ports
Adjust Manifold Pressure
1. Adjust manifold pressure to obtain proper gas input rate.
See Fig. 61.
a. Refer to the correct manifold pressure table for the appro-
priate model.
b. Turn gas valve ON/OFF switch to OFF.
c. Loosen set screw on manifold tower pressure tap no
more than one full turn with a 3/32--in. hex wrench, or
remove the 1/8 inch NPT plug from the manifold pres-
sure tap on the gas valve.
d. Connect a water column manometer or similar device to
manifold pressure tap.
e. Turn gas valve ON/OFF switch to ON.
f. Manually close blower door switch.
