EXAMPLE: (0—2000 ft altitude using Table 9)
Heating value = 1050 Btu/cu ft
Specific gravity = 0.62
Therefore: Orifice No. 45
Manifold pressure 3.6-in. wc
* Furnace is shipped with No. 45 orifices. In this example
all main burner orifices are the correct size and do not need
to be changed to obtain the proper input rate.
2. Check and verify burner orifice size in furnace. NEVER
ASSUME ORIFICE SIZE; ALWAYS CHECK AND
VERIFY.
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.
3. Change orifice if required or proceed to Item 4.
a. Turn off gas and electrical supplies to furnace.
b. Remove main furnace door.
c. Turn furnace gas valve control knob or switch to OFF
position.
d. Remove burner enclosure front.
e. Remove gas supply pipe from gas valve.
f. Remove wires from gas valve. Note location for reas-
sembly.
CAUTION:
Label all wires prior to disconnection when
servicing controls. Wiring errors can cause improper and
dangerous operation.
ATTENTION: Lors des opérations d’entretien des com-
mandes, étiqueter tous les fils avant de les déconnecter.
Toute erreur de câblage peut être une source de danger et
de panne.
g. Remove burner enclosure pressure tube from gas valve
burner enclosure reference pressure tap fittings. (See
Fig. 31.)
h. Remove screws securing manifold to burner box. Re-
move manifold, orifices, and gas valve as 1 assembly.
i. Obtain new natural gas orifices from authorized factory
parts distributor.
j. Remove natural gas orifices from manifold and place
them in the bag supplied marked "Natural Gas Orifices."
Manufactured (mobile) home installations are required to
have these materials located with furnace for future
conversion.
k. Install main burner orifices. Do not use Teflon tape.
Finger-tighten orifices at least 1 full turn to prevent
cross-threading, then tighten with wrench. There are
enough orifices in each kit for the largest furnace.
Orifices of other sizes must be field supplied and are
available through your local distributor.
l. Reinstall manifold, orifices, and gas valve assembly in
burner box. Ensure manifold seal is installed properly
and burners fit over orifices. (See Fig. 32.)
m. Reconnect wires to gas valve. Refer to furnace wiring
schematic or as labeled earlier for proper wire location.
n. Reinstall burner enclosure pressure tube to gas valve
burner enclosure reference pressure tap. (See Fig. 31.)
o. Reinstall gas supply pipe to gas valve using backup
wrench to prevent rotation and improper orientation.
NOTE:
Use propane-gas-resistant pipe dope to prevent gas leaks.
DO NOT use Teflon tape.
WARNING:
Gas valve knob or switch MUST be facing
forward or tilted upward. Failure to follow this warning
could result in property damage, personal injury, or death.
Fig. 31—Redundant Convertible Automatic Gas Valve
A99048
MANIFOLD
PRESSURE TAP
REGULATOR PLUNGER
BURNER
ENCLOSUR
REFERENC
PRESSURE
TAP
LP/NAT
CONVERTIBLE
CAP
INLET
PRESSURE
TAP
LP
NAT
ON/OFF
SWITCH
CAUTION:
DO NOT redrill orifices. Improper drilling
(burrs, out-of-round holes, etc.) can cause excessive
burner noise and misdirection of burner flames. This can
result in flame impingement of burners and heat exchang-
ers causing failures.
A93059
BURNER
ORIFICE
—28—
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