International comfort products N9MSE0401410A Service And Technical Support Manual page 5

SERVICE AND TECHNICAL SUPPORT MANUAL
Figure 2 Orifice Hole
For proper operation and long term reliability the furnace input
rate must be within +/−2 percent of input rate on furnace rating
plate.
The gas input rate on rating plate is for installation at altitudes
up to 2000 ft. (610 M)
In the U.S.A., the input rating for altitudes above 2000 ft. (610
M) must be reduced by 2 percent for each 1000 ft. (305 M)
above sea level refer to Table 1.
In Canada, the input rating must be derated by 5 percent for
altitudes of 2000 ft. (610 M) to 4500 ft. (1372 M) above sea
level.
To adjust manifold pressure to obtain the proper input rate, first,
determine if the furnace has the correct orifice installed. At
higher altitudes or different gas heat contents, it may be
necessary to change the factory orifice to a different orifice.
Tables have been provided in the furnace Service and
Technical Manual to match the required orifice to the manifold
pressure to the heat content and specific gravity of the gas. To
do this:
a. Obtain average yearly gas heat value (at installed
altitude) from local gas supplier.
b. Obtain average yearly gas specific gravity from local
gas supplier.
c. Find installation altitude range for your installation in
the manifold pressure tables in Table 3.
d. Find closest natural gas heat value and specific
gravity in Table 3.
e. Follow heat value and specific gravity lines to point of
intersection to find orifice size and manifold pressure
setting for proper operation.
f. Check and verify burner orifice size in furnace.
NEVER ASSUME ORIFICE SIZE. ALWAYS CHECK
AND VERIFY.
g. Replace orifice with correct size, if required by
Table 3. Use only factory−supplied orifices. See
EXAMPLE.
EXAMPLE: 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.
* 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.
1. Adjust manifold pressure to obtain input rate. (See
Figure 3)
a. Turn gas valve ON/OFF switch to OFF.
440 04 4401 00
Table 1
ALTITUDE
2001–3000
3001–4000
BURNER
(914−1219)
ORIFICE
4001–5000
(1219−1524)
5001–6000
A93059
(1524−1829)
6001–7000
(1829−2134)
7001–8000
(2134−2438)
8001–9000
(2438−2743)
9001–10,000
(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)
NOTE: 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.
NOTE: DO NOT set manifold pressure less than 3.2 in. w.c. or
more than 3.8 in. w.c. for natural gas. If manifold pressure is
outside this range, change main burner orifices to obtain
manifold pressure in this range.
Figure 3
1/8" NPT Inlet
Pressure Tap
Specifications subject to change without notice.
b. Remove manifold pressure tap plug from gas valve.
c. Connect a water column manometer or similar device
to manifold pressure tap.
d. Turn gas valve ON/OFF switch to ON.
e. Manually close blower door switch.
f. Jumper R and W thermostat connections on control
to start furnace. (See Figure 4)
Altitude Derate Multiplier for U.S.A.
PERCENT
FT. (M) OF DERATE
0–2000
0
(0−610)
4−6
(610−914)
6−8
8−10
10−12
12−14
14−16
16−18
18−20
g. Remove regulator adjustment cap from gas valve
pressure regulator (See Figure 3) and turn adjusting
screw (3/16 or smaller flat−tipped screwdriver)
counterclockwise (out) to decrease input rate or
clockwise (in) to increase input rate.
Redundant Automatic Gas Valve
(Single Stage)
ON/OFF Switch
1/2" NPT Inlet
Gas Furnace: N9MSE
DERATE MULTIPLIER
FACTOR*
1.00
0.95
0.93
0.91
0.89
0.87
0.85
0.83
0.81
Regulator Seal Cap
Regulator Adjustment
Regulator Seal Cap under Cap
1/2" NPT Outlet
1/8" NPT Manifold
Pressure Tap
A11153
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