68
The NATURAL GAS manifold pressure adjustments in Table
21 compensate for BOTH altitude AND gas heating value.
DO NOT apply an additional derate factor to the pressures
shown in Table 21.
The values in this table are NOT
referenced to sea level; they are AS--MEASURED AT
ALTITUDE.
The heating content of natural gas at altitude may already
provide for a reduction in capacity of the furnace. Be sure to
obtain the expected in--season gas heating value of the gas
from the gas supplier BEFORE making any adjustments for
capacity or altitude. Refer to Table 21. No adjustments to the
furnace may be necessary at altitude for certain gas heating
values.
Refer to the instructions provided in the factory--specified
LP/Propane conversion kit for instructions for setting gas
manifold pressures for LP/Propane applications.
NOTICE
In the USA, the input rating for altitudes above 2000 ft. (609.6M)
must be reduced by 2 percent for each 1000 ft. (304.8M) above sea
level. Refer to Table 18. The natural gas manifold pressures in
Table 21 adjust for BOTH altitude and natural gas heating value.
In Canada, the input rating must be reduced by 5 percent for
altitudes of 2000 ft. (609.6M) to 4500 ft. (1371.6M) above sea
level. The natural gas manifold pressures in Table 21 adjust for
BOTH altitude and natural gas heating value.
NOTE
: For Canadian altitudes of 2000 to 4500 ft. (609.6 to
1371.6M), Use USA altitudes of 2001 to 3000 ft. (609.6 to
914.4M).
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 installation instructions to match the
required orifice to the manifold pressure to the heat content and
specific gravity of the gas. To do this:
1. Obtain average yearly gas heat value (at installed altitude)
from local gas supplier.
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.
5. 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.
6. 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
7. Replace orifice with correct size, if required as shown in
Table 21. Use only factory--supplied orifices. See
EXAMPLE 1.
EXAMPLE 1
EXAMPLE: 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) for high heat, 1.4--in. w.c.
(349 Pa) for low heat
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.
for natural gas. The maximum inlet gas pressure is 13.6 in. of water
column. If the inlet pressure is too low, you will not be able to
adjust the manifold pressure to obtain the proper input rate. To
check the inlet gas pressure:
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 the R to W/W1 and W2 thermostat connections at
the furnace control board.
8. When main burners ignite, confirm inlet gas pressure is
Between 4.5 in. w.c. and 13.6 in. w.c.
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
⅛
--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
⅛
--in. NPT plug was removed, apply pipe
dope sparingly to end of plug and re--install in the gas
valve.
Adjust Manifold Pressure
1. Adjust manifold pressure to obtain low fire input rate. See
Fig. 61.
a. Turn gas valve ON/OFF switch to OFF.
b. Loosen set screw on manifold tower pressure tap with
3/32--in. hex wrench, or remove the 1/8 inch NPT plug
from the manifold pressure tap on the gas valve.
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Страница 74: ...74 A190155 Fig 65 Furnace Setup Switches and Description Continued ...
Страница 91: ...91 A190153 Fig 72 Wiring Diagram ...