Carrier WeatherMaster Puron 48HC D17, Service And Maintenance Instructions, Page: 34 / 100

34
LIQUID PROPANE
Accessory packages are available for field-installation that will
convert the 48HC 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 on page 38 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. See Table 12. 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 [Normally
Open]) will open the gas valve power whenever the supply line
pressure drops below the setpoint. See Fig. 42 and 43. The
switch, HK02LB008, opens contacts on pressure “fall” at
7.2 in. wg ± 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 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 recy-
cle of unit power after the low pressure switch has closed.
LIMIT SWITCH
Remove blower access panel. Limit switch is located on the
fan deck for sideshot units and on the vestibule plate for down-
shot units. See Fig. 41.
This switch also prevents operation when the propane tank lev-
el is low which can result in gas with a high concentration of
impurities, additives, and residues that have settled to the bot-
tom 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. 42 — LP Low Pressure Switch (installed) for
48HC*D
Fig. 43 — LP Supply Line Low Pressure Switch
Wiring
Flue Gas Passageways
To inspect the flue collector box and upper areas of the heat
exchanger:
1. Remove the combustion blower wheel and motor assem-
bly according to directions in Combustion-Air Blower sec-
tion. See Fig. 44.
2. Remove the flue cover to inspect the heat exchanger.
3. Clean all surfaces as required using a wire brush.
Combustion-Air Blower
Clean periodically to assure proper airflow and heating effi-
ciency. Inspect blower wheel every fall and periodically during
heating season. For the first heating season, inspect blower
wheel bi-monthly to determine proper cleaning frequency.
To access burner section, open the heater access door below the
indoor fan panel.
To inspect blower wheel, shine a flashlight into draft hood
opening. If cleaning is required, remove motor and wheel as
follows:
1. Remove the seven screws attaching the induced-draft
motor housing to the vestibule plate. See Fig. 44.
2. The blower wheel can be cleaned at this point. If additional
cleaning is required, continue with Steps 3 through 5.
3. Remove the blower from the motor shaft, by loosening
two setscrews.
4. Remove the motor by removing the four screws that hold
the motor to mounting plate. Remove the motor cooling
fan by removing one setscrew.
5. Remove the nuts that hold the motor to the mounting plate.
6. To reinstall, reverse the procedure outlined above.
Table 9 — Natural Gas Supply Line Pressure Ranges
UNIT MODEL UNIT SIZE MIN MAX
48HC
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
RANGE
48HC
All 3.0 in. wg 2.0 in. wg Reference MRT unit nameplate
for range ratings.
Table 11 — Liquid Propane Supply Line Pressure
Ranges
UNIT MODEL UNIT SIZE MIN MAX
48HC
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
48HC
All
11.0 in. wg
(2740 Pa)
7.3 in. wg
(1820 Pa)
LP LOW PRE SS URE
S WITCH
GA S VALVE
PNK W2
TSTAT
GRA
BRN
IGC
J2-12
IGC
J2-11
BRN
C
NO
MGV
C
LP LPS