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23
Limit Switch
and Shield
C08284
Fig. 28 -- Limit Switch Location
Fuel Types and Pressures
Natural Gas — The 48TC 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
48TC All
4.0 in. wg
(996 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 Manifol d Pressure Ranges
UNIT
MODEL
UNIT
SIZE
HIGH
FIRE
LOW
FIRE
RANGE
48TCD,S
48TCE,R
48TCF,T
All
3.5 in. wg
(872 Pa)
1.7 in. wg
(423 Pa){
2.0---5.0 in. wg (Hi)
(498---1245 Pa)
48TCL
48TCM
48TCN
All
3.5 in. wg
(872 Pa)
NA
2.0---5.0 in. wg (Hi)
(498---1245 Pa)
NA: Not Available
{ 3 Phase models only
Liquid Propane — Accessory packages are available for
field--installation that will convert the 48TC 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.
Table 6 – Liquid Propane Supply Line Pressure Ranges
UNIT MODEL UNIT SIZE MIN MAX
48TCD,E,F
48TCS,R,T
All
11.0 in. wg
(2740 Pa)
13.0 in. wg
(3240 Pa)
48TCL,M,N All NA NA
Manifold pressure for LP fuel use must be adjusted to
specified range. Follow instructions in the accessory kit to
make initial readjustment.
Table 7 – Liquid Propane Manifold Pressure Ranges
UNIT MODEL UNIT SIZE HIGH FIRE LOW FIRE
48TCD,S
48TCE,R
48TCF,T
All
10.0 in. wg
(2490 Pa)
5.0 in. wg
(1245 Pa){
48TCL,
48TCM,
48TCN
All NA NA
NA: Not Available
{ 3 Phase models only
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. 29 and Fig. 30. 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 requires a
recycle of unit power after the low pressure switch has
closed.
C08238
Fig. 29 -- LP Low Pressure Switch (Installed)
PNK
W2
TSTAT
GRA
BRN
IGC
J2-12
IGC
J2-11
BRN
C
NO
MGV
C
LP LPS
C08285
Fig. 30 -- LP Supply Line Low Pressure Switch Wiring
48TC