22
Fig. 30 — Burner Section Details
Fig. 31 — Limit Switch Location
Fuel Types and Pressures
NATURAL GAS
The 48LC unit is factory-equipped for use with Natural Gas (NG)
fuel at elevation under 2000 ft (610 m). See Orifice Replacement
section for information in modifying this unit for installation at el-
evations above 2000 ft (610 m).
Gas line pressure entering the unit’s main gas valve must be within
specified ranges (see Table 4). Adjust unit gas regulator valve as
required or consult local gas utility.
Manifold pressure is factory-adjusted for NG fuel use. Adjust as
required to obtain best flame characteristic (see Table 5).
LIQUID PROPANE
Accessory packages are available for field-installation that will
convert the 48LC unit (except low NOx models) to operate with
Liquid Propane (LP) fuels. These kits include new orifice spuds,
new springs for gas valves and a supply line low pressure switch.
See section on Orifice Replacement for details on orifice size se-
lections.
Low NOx models include specially-sized orifices and use of dif-
ferent flue flow limits and tube baffles. Because of these extra fea-
tures, conversion of these models to LP is not recommended.
Fuel line pressure entering unit gas valve must remain within
specified range (see Table 6).
Manifold pressure for LP fuel use must be adjusted to specified
range (see Table 7). Follow instructions in the accessory kit to
make initial readjustment.
SUPPLY PRESSURE SWITCH
The LP conversion kit includes a supply low pressure switch. The
switch contacts (from terminal C to terminal NO) will open the
gas valve power whenever the supply line pressure drops below
the setpoint. See Fig. 32 and 33. If the low pressure remains open
for 15 minutes during a call for heat, the IGC circuit will initiate a
Ignition Fault (5 flashes) lockout. Reset of the low pressure switch
is automatic on rise in supply line pressure. Reset of the IGC re-
quires a recycle of unit power after the low pressure switch has
closed.
This switch also prevents operation when the propane tank level is
low which can result in gas with a high concentration of impuri-
ties, additives, and residues that have settled to the bottom of the
tank. Operation under these conditions can cause harm to the heat
exchanger system. Contact your fuel supplier if this condition is
suspected.
Fig. 32 — LP Low Pressure Switch (Installed)
INDUCED-
DRAFT
MOTOR
MOUNTING
PLATE
INDUCED-
DRAFT
MOTOR
MANIFOLD
PRESSURE
TAP
VESTIBULE
PLATE
FLUE
EXHAUST
ROLLOUT
SWITCH
BLOWER
HOUSING
GAS
VALVE
BURNER
SECTION
Limit Switch
and Shield
Table 4 — Natural Gas Supply Line Pressure Ranges
UNIT MODEL UNIT SIZE MIN MAX
48LCD/E/L/M/S/R* 04, 05, 06
4.0 in. wg
(996 Pa)
13.0 in. wg
(3240 Pa)
48LCF/N/T*
(High Heat units only)
05, 06
5.0 in. wg
(1245 Pa)
13.0 in. wg
(3240 Pa)
Table 5 — Natural Gas Manifold Pressure Ranges
UNIT MODEL UNIT SIZE MIN MAX
48LCD/E/L/M/S/R* 04, 05, 06
3.5 in. wg
(872 Pa)
1.7 in. wg
(423 Pa)
48LCF/N/T*
(High Heat units only)
05, 06
3.5 in. wg
(872 Pa)
1.7 in. wg
(423 Pa)
Table 6 — Liquid Propane Supply Line Pressure
Ranges
UNIT MODEL UNIT SIZE MIN MAX
48LCD/E/L/M/S/R* 04, 05, 06
11.0 in. wg
(2740 Pa)
13.0 in. wg
(3240 Pa)
48LCF/N/T*
(High Heat units only)
05, 06
11.0 in. wg
(2740 Pa)
13.0 in. wg
(3240 Pa)
Table 7 — Liquid Propane Manifold Pressure Ranges
UNIT MODEL UNIT SIZE MIN MAX
48LCD/E/L/M/S/R* 04, 05, 06
10.0 in. wg
(2490 Pa)
5.0 in. wg
(1245 Pa)
48LCF/N/T*
(High Heat units only)
05, 06
10.0 in. wg
(2490 Pa)
5.0 in. wg
(1245 Pa)
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