Carrier 48TC series, Инструкции по обслуживанию и техническому обслуживанию, Страница: 33 / 112

33
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.
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.
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
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.
Fig. 47 — LP Low Pressure Switch (Installed)
Fig. 48 — LP Supply Line Low Pressure Switch
Wiring
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.
Table 9 — 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)
Table 10 — Natural Gas Manifold Pressure Ranges
UNIT MODEL UNIT SIZE HIGH FIRE LOW FIRE
48TC
All 3.0 in. wg (747 Pa) 2.0 in. wg (498 Pa)
Table 11 — Liquid Propane Supply Line Pressure
Ranges
UNIT MODEL UNIT SIZE MIN MAX
48TC All
11.0 in. wg
(2740 Pa)
13.0 in. wg
(3240 Pa)
Table 12 — Liquid Propane Manifold Pressure
Ranges
UNIT MODEL UNIT SIZE HIGH FIRE LOW FIRE
48TC All
11.0 in. wg
(2740 Pa)
7.3 in. wg
(1817 Pa)
LP LOW PRESSURE
SWITCH
GAS VALVE
PNK
W2
TSTAT
GRA
BRN
IGC
J2-12
IGC
J2-11
BRN
C
NO
MGV
C
LP LPS