Check Inlet Gas Pressure; Adjust Manifold Pressure - International comfort products N9MSE0261408A Service And Technical Support Manual

SERVICE AND TECHNICAL SUPPORT MANUAL
2. Obtain average yearly gas specific gravity from local gas
supplier.
3. Find installation altitude range for your installation in the
manifold pressure tables in Table 3 or Table 4.
4. Find closest natural gas heat value and specific gravity in
Table 3 or Table 4. Follow heat value and specific
gravity lines to point of intersection to find orifice size and
low-and high-heat manifold pressure settings for proper
operation.
5. Check and verify burner orifice size in furnace. NEVER
ASSUME ORIFICE SIZE. ALWAYS CHECK AND
VERIFY.
NOTICE
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.
6. Replace orifice with correct size, if required by Table 3 or
Table 4. Use only
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
(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.)
Manifold pressure: 3.4-in. w.c. (847 Pa).
NOTE: To convert gas manifold Table pressures to Pascals,
multiply the in.w.c. value by 249.1 Pa/in. w.c. (1 in. wc. = 249.1
Pa).
Table 1 Altitude Derate Multiplier for USA
ALTITUDE PERCENT
FT. (M) OF DERATE
0–2000
0
(0−610)
2001–3000
4−6
(610−914)
3001–4000
6−8
(914−1219)
4001–5000
8−10
(1219−1524)
5001–6000
10−12
(1524−1829)
6001–7000
12−14
(1829−2134)
7001–8000
14−16
(2134−2438)
8001–9000
16−18
(2438−2743)
9001–10,000
18−20
(2743−3048)
* Derate multiplier factors are based on midpoint altitude for altitude range.
NOTE: For Canadian altitudes of 2000 to 4500 ft. (610 to
1372 M), use USA altitudes of 2001 to 3000 ft. (610 to 914
M)

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.
6
factory−supplied orifices.
DERATE MULTIPLIER
FACTOR*
1.00
0.95
0.93
0.91
0.89
0.87
0.85
0.83
0.81
Specifications subject to change without notice.
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.
See
12. Turn off furnace power supply.
13. Remove manometer from the inlet pressure tap of the
gas valve.
WARNING
!
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.
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.

Adjust Manifold Pressure

There are two manifold pressure tables in these
NOTE:
instructions. USE TABLE 3 FOR THE LOW CAPACITY 26,000
BTUH MODELS. The low capacity model can be identified by
the green label affixed to the top of the gas valve. For all other
models use Table 4.
1. Adjust manifold pressure to obtain proper gas input rate.
(See Figure 3)
a. Refer to the correct manifold pressure table for the
appropriate 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
pressure tap on the gas valve. See Figure 3.
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.
g. Jumper R and W thermostat connections on control
to start furnace. (See Figure 4)
h. Remove regulator adjustment cap from gas valve
pressure regulator and turn adjusting screw (3/16 or
smaller flat−tipped screwdriver) counterclockwise
(out) to decrease input rate or clockwise (in) to
increase input rate. (See Figure 3)
Gas Furnace: N9MSE
440 04 4402 06