Sears 9MPD - Manual (Page 30)

5. Gas Supply and Piping
CARBON MONOXIDE POISONING, FIRE AND EXPLO­
SION HAZARD
Models designated for Natural Gas are to be used
with Natural Gas Only, unless properly converted
to use with LP gas.
Furnace operating with the wrong fuel result in death,
personal injury and/or property damage.
NOTE: The rating plate is stamped with the model number, gas
type and gas input rating. In addition, models manufactured for
sale in Canada have orifice size information stamped on the rat­
ing plate.
Alternate BTUH Input Ratings (USA Only)
The input rating of these furnaces can be changed from the stan­
dard input rating to the alternate input rating shown in
Table 5, by
changing the main burner orifices. NOTE: The input rating ot
80,000 BTUH models cannot be changed from the standard in­
put. Changing of burner orifices MUST be done by a qualified ser­
vice technician. See section on changing orifices or following
page.
Table .5 Alternate Input Ratings, USA ONLY.
BTUH
Standard
Rating
BTUH
Alternate
Rating
Natural
Gas
Orifice
LP
Gas
Orifice
50,000 40,000 #44 #55
75,000 60,000 #44 #55
100,000 80,000 #44 #55
125,000 100,000 #44 #55
Supply Pressure
FIRE HAZARD
Failure to properly set input pressure can result in
death, personal injury and/or property damage.
Do NOT set input rating above that shown on rating
plate.
1. Supply pressure can be checked using the Vg" NPT port
on the supply side of the gas valve.
2. Gas input to burners MUST NOT exceed the rated input
shown on rating plate.
3. Do NOT allowminimumgassupply pressure to vary down­
ward. Doing so will decrease Input to furnace. Refer to
Table 6 for normal gas supply and manifold pressures.
Table 6 Gas Pressures Below 2000'
Gas
Type
Supply Pressure Manifold
Pressure
Recommended Max. Min.
Natural 7" 14” 4.5" 3.5"
LP 11” 14” 11” 10"
Important Note:
• With Propane gas, the rated input is obtained when the
BTU content is 2,500 BTU per cubic foot and manifold
pressure set at 10" W.C.
• If Propane gas has a different BTU content, orifices
MUST be changed by licensed Propane installer.
• Measured input can NOT exceed rated input.
• Any major change in gas flow requires changing burn­
er orifice size.
Gas Supply Pressure
Gas supply pressure should be within minimum and maximum
values listed on rating plate. Pressures are usually set by gas sup­
pliers.
Manifold Gas Pressure Adjustment
NOTE: Make adjustment to manifold pressure with burners oper­
ating.
FIRE OR EXPLOSION HAZARD
Failure to turn OFF gas at shut off before connecting
manometer can result in death, personal injury and/or
property damage.
Turn OFF gas at shut off before connecting manometer.
1. Remove the burner compartment door.
2. With gas OFF, connect manometer to tapped opening on
gas valve. Use manometer with a 0 to 15" water column
range.
3. Turn gas ON and remove adjustment screw cover on gas
valve. Turn counterclockwise to decrease pressure and
clockwise to increase.
4. For altitudes up to 2000', set pressure to value shown In
Table 6, ± 0.3' water column.
5. Connect manometer to the tapped opening on the outlet
side of gas valve. Use manometer with a 0-15 ' min. water
column range.
6
. Turn gas ON, fire the furnace and remove adjustment
screw cover on gas valve.
7. Turn counterclockwise to decrease pressure and clock­
wise to increase.
8
. SetpressuretovalueshowninTable 6. Refer to Important
Notes in Table 6. Pressure is also listed on furnace rating
plate.
9. When pressure is set, replace adjustment screw cover on
gas valve.
10. Replace the burner compartment door.
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