Fuel Types And Pressures; Flue Gas Passageways - Carrier WeatherMaker 48TC Series Service And Maintenance Instructions

Fuel Types and Pressures

NATURAL GAS
The 48TC unit is factory-equipped for use with Natural Gas (NG)
fuel at elevation under 2000 ft (610 m). See section Orifice Re-
placement 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. See Table 9.
Manifold pressure is factory-adjusted for NG fuel use. Adjust as
required to obtain best flame characteristic. See Table 10.
Table 9 — Natural Gas Supply Line Pressure Ranges
UNIT MODEL UNIT SIZE
48TC All
Table 10 — Natural Gas Manifold Pressure Ranges
UNIT MODEL UNIT SIZE
48TC
All
LIQUID PROPANE
Accessory packages are available for field-installation that will
convert the 48TC unit 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 Re-
placement for details on orifice size selections.
Fuel line pressure entering unit gas valve must remain within
specified range. See Table 11.
Manifold pressure for LP fuel use must be adjusted to specified
range. Follow instructions in the accessory kit to make initial read-
justment. See Table 12.
Table 11 — Liquid Propane Supply Line Pressure
Ranges
UNIT MODEL UNIT SIZE
48TC All
Table 12 — Liquid Propane Manifold Pressure
Ranges
UNIT MODEL UNIT SIZE
48TC All
SUPPLY PRESSURE SWITCH
The LP conversion kit includes a supply low pressure switch.
The switch contacts (from terminal C to terminal NO [Normal-
ly Open]) will open the gas valve power whenever the supply
line pressure drops below the setpoint. See Fig. 47 and Fig. 48.
The switch, HK02LB008, opens contacts on pressure "fail" at
7.2 ± 0.70 in. wg. Contacts close on pressure rise above
10.2 in. wg. If the low pressure remains open for 15 minutes
during a call for heat, the IGC circuit will initiate an Ignition
Fault (5 flashes) lockout. Reset of the low pressure switch is
MIN MAX
4.0 in. wg 13.0 in. wg
(996 Pa) (3240 Pa)
HIGH FIRE LOW FIRE
3.0 in. wg (747 Pa) 2.0 in. wg (498 Pa)
MIN MAX
11.0 in. wg 13.0 in. wg
(2740 Pa) (3240 Pa)
HIGH FIRE LOW FIRE
11.0 in. wg 7.3 in. wg
(2740 Pa) (1817 Pa)
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.
LIMIT SWITCH
Remove the blower access panel. The Limit Switch is located on
the fan deck for sideshot units and on the vestibule plate for down-
shot units. See Fig 47.
GAS VALVE
Fig. 47 — LP Low Pressure Switch (Installed)
IGC
BRN
J2-11
IGC
J2-12
TSTAT
W2
Fig. 48 — LP Supply Line Low Pressure Switch
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.

Flue Gas Passageways

To inspect the flue collector box and upper areas of the heat
exchanger:
1. Remove the combustion blower wheel and motor assembly
according to directions in the Combustion-Air Blower sec-
tion. See Fig. 49.
2. Remove the flue cover to inspect the heat exchanger.
3. Clean all surfaces as required using a wire brush.
33
LP LOW PRESSURE
SWITCH
LP LPS
BRN
C
NO
MGV
GRA
PNK
Wiring
C