23
The standard supply fan motor is equipped with internal
overcurrent and overtemperature protection. Protection
devices reset automatically.
The High Static option supply fan motor is equipped with
a pilot--circuit Thermix combination overtemperature/
overcurrent protection device. This device resets
automatically. Do not bypass this switch to correct
trouble. Determine the cause and correct it.
Condenser Fan Motor Protection
The condenser fan motor is internally protected against
overtemperature.
Relief Device
A soft solder joint at the suction service access port
provides pressure relief under abnormal temperature and
pressure conditions (i.e., fire in building). Protect this
joint during brazing operations near this joint.
Control Circuit, 24--V
The control circuit is protected against overcurrent
conditions by a circuit breaker mounted on control
transformer TRAN. Reset is manual.
GAS HEATING SYSTEM
General
The heat exchanger system consists of a gas valve feeding
multiple inshot burners off a manifold. The burners fire
into matching primary tubes. The primary tubes discharge
into combustion plenum where gas flow converges into
secondary tubes. The secondary tubes exit into the
induced draft fan wheel inlet. The induced fan wheel
discharges into a flue passage and flue gases exit out a
flue hood on the side of the unit. The induced draft fan
motor includes a Hall Effect sensor circuit that confirms
adequate wheel speed via the Integrated Gas Control
(IGC) board. Safety switches include a Rollout Switch (at
the top of the burner compartment) and a limit switch
(mounted through the fan deck, over the tubes). (See Fig.
30 and Fig. 31.)
INDUCED-
DRAFT
MOTOR
MOUNTING
PLATE
INDUCED-
DRAFT
MOTOR
MANIFOLD
PRESSURE
TAP
VESTIBULE
PLATE
FLUE
EXHAUST
ROLLOUT
SWITCH
BLOWER
HOUSING
GAS
VALVE
BURNER
SECTION
C06152
Fig. 30 -- Burner Section Details
Limit Switch
and Shield
C08284
Fig. 31 -- Limit Switch Location
Fuel Types and Pressures
Natural Gas — The 48LC unit is factory--equipped for use
with Natural Gas fuel at elevation under 2000 ft (610 m).
See section Orifice Replacement for information in
modifying this unit for installation at elevations above
2000 ft (610 m).
Gas line pressure entering the unit’s main gas valve must
be within specified ranges. Adjust unit gas regulator valve
as required or consult local gas utility.
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)
Manifold pressure is factory--adjusted for NG fuel use.
Adjust as required to obtain best flame characteristic.
Table 5 – Natural Gas Manifold Pressure Ranges
UNIT MODEL UNI T SIZ E HIGH FIRE LOW FIRE
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)
Liquid Propane — Accessory packages are available for
field--installation that will convert the 48LC unit (except
low NO
x
model) 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
selections.
Low NO
x
models include specially--sized orifices and use
of different flue flow limits and tube baffles. Because of
these extra features, conversion of these models to LP is
not recommended.
Fuel line pressure entering unit gas valve must remain
within specified range.
48LC
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