Adjusting Or Checking Furnace Input - Rheem RGPE series Installation Instructions Manual

• The controller sends a spark signal to
spark across the electrodes.
• The main solenoid on the gas valve
are energized (low fire) allowing gas to
flow to the burners.
• When flame is proven, the ignition
control is de-energized - 8 second
maximum trial time.
• The gas valve maintains low rate
through the warm-up period - 20 sec-
onds (aka Blower Off Delay).
Heating Cycle Response
® TWO-STAGE FUNCTION – NON-
COMMUNICATING SYSTEMS ONLY:
(Two-stage function only applies when
SW1-3 is in the "OFF" position and a
two-stage thermostat is installed as
shown in Figure 49.)
After the warm-up period, the furnace
will respond to the thermostat demand
by adjusting the gas valve and blower
heating speeds to the "W" signal val-
ues. "W" only = low gas valve pressure
and blower heating speed. "W2" = high
gas valve pressure and blower heating
speed if the call for heat ends, the fur-
nace terminates at the present rate.
® SINGLE-STAGE FUNCTION – NON-
COMMUNICATING SYSTEMS ONLY:
(SW2-2 and SW2-3 must both be
turned "off" for this operation.)
("W" signal only)
After the warm-up period, the furnace
will respond to the thermostat demand
by altering the gas valve pressure and
blower speed as follows:
Phase 1: 0 to 7 minutes = Low fire fur-
nace capacity (gas valve output and
blower speed)
Phase 2: After 7 minutes = 100% of fur-
nace capacity (gas valve output and
blower speed)
NOTE: If the call for heat ends during
any phase, the furnace will terminate
immediately at the firing rate of that
phase.
Heating Cycle Termination
("W" signal only, refer to dip switch set
SW2 on IFC)
When the 24 volt signal is removed from
W1 or, for communicatiing systems, a
message is transmitted from the thermo-
stat to the furnace to "end the heat call",
the heating cycle will end and the fur-
nace will shut down and return to the
proper off cycle operation.
ADJUSTING OR CHECKING
FURNACE INPUT
NATURAL GAS:
The maximum gas supply pressure to
the furnace should be 10.5" W.C. for
natural gas. The minimum gas supply
pressure for purposes of input adjust-
ment to the furnace should be 5" W.C.
A properly calibrated manometer or
gauge is required for accurate gas pres-
sure readings.
1. When adjusting the furnace input, the
high fire input should be checked.
The high fire manifold pressure
should be 3.5' W.C. Follow these
steps to be sure the furnace is high
fire mode:
a. With a single stage thermostat, the
furnace runs for 12 minutes on low
fire before shifting to high fire. To
be certain that it is on high fire,
jump terminals "W" and "W2" on
the control board in the blower
compartment.
b. With a two stage thermostat, set
the thermostat to its highest setting
to keep the furnace operating in
the high fire mode.
2. To adust high fire manifold pressure,
remove the adjustment cover screw
on the outlet end of the gas valve
and turn the adjustment screw clock-
wise to increase the pressure and
counterclockwise to reduce the pres-
sure. Replace the cover screw
securely.
3. The low fire manifold pressure should
be 1.7" W.C. As mentioned above,
the furnace remains in the low fire
mode for 12 minutes upon a heat call
with a single stage thermostat. With a
two stage thermostat, disconnect the
thermostat lead to the "W2" terminal
on the control board and the furnace
will remain in the low fire mode. To
adjust the pressure, remove the regu-
lator cover, on top of the valve, and
adjust as noted under Step 2, above.
After the adjustment replace the
screw cover securely.
TABLE 18
METER TIME IN MINUTES AND SECONDS FOR NORMAL
INPUT RATING OF FURNACES EQUIPPED FOR NATURAL OR LP GAS
METER
INPUT
SIZE
BTU/HR
CU. FT.
ONE
50,000
TEN
ONE
75,000
TEN
ONE
100,000
TEN
ONE
125,000
TEN
ONE
150,000
TEN
Heating Value of Gas (BTU/Ft
Input BTU/HR =
Time in Seconds (for 1 cu.ft.) of Gas
NOTE: Use a 3/32 allen wrench for
making the pressure adjustment.
LP GAS:
Furnaces for use on LP gas, the LP
gas supply pressure must be set
between 11.0" and 13.0" W.C. by
means of the tank or branch supply
regulators. The furnace manifold
pressure should be set at 10" W.C.
at the gas control valve. For eleva-
tions up to 7,000 feet, rating plate
input ratings apply. For high altitudes
(elevations 7,000 and over) and for
any necessary major changes in the
gas flow rate the orifice spud must
be changed.
TO CHANGE ORIFICE SPUDS:
1. Shut off the manual main gas
valve and remove the gas mani-
fold.
2. Replace the orifice spuds.
3. Reassemble in reverse order.
4. Turn the gas supply back on and
check for leaks.
5. Check for proper operation and
set to proper manifold pressure.
Check of input is important to pre-
vent over firing of the furnace
beyond its design-rated input.
NEVER SET INPUT ABOVE THAT
SHOWN ON THE RATING PLATE.
TO CHECK FURNACE INPUT:
1. Make certain that all other gas
appliances are shut off, with the
exception of pilot burners.
2. Start the furnace
3. Time the meter to measure the
time required to burn one cubic
foot of gas.
4. Use Table 4 to determine input
rate.
HEATING VALUE OF GAS BTU PER CU. FT.
900 1000 1040
MIN. SEC. MIN. SEC. MIN. SEC. MIN. SEC. MIN. SEC.
1 5 1 12 1 15
10 50 12 00 12 30
0 44 0 48 0 50
7 12 8 0 8 19
0 33 0 36 0 38
5 24 6 0 6 15
0 26 0 29 0 30
4 19 4 48 5 0
0 31 0 24 0 25
3 36 4 0 4 10
3 ) x 3600 x correction factor
1100 2500
1 18 3 20
13 12 30 00
0 53 2 0
8 48 20 0
0 40 1 30
6 36 15 0
0 32 1 12
5 17 12 0
0 26 1 0
4 20 10 0
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