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506526-01Page 30 of 39 Issue 1031
Heating Sequence Of Operation (Figure 36)
1. When thermostat calls for heat, combustion air blower
starts.
2. Combustion air pressure switch proves blower operation.
Switch is factory set and requires no adjustment.
3. After a 15 second prepurge, the hot surface ignitor
energizes.
4. After a 20 second ignitor warm-up period, the gas valve
solenoid opens. A 4 second trial for ignition period
begins.
5. Gas is ignited, flame sensor proves the flame, and the
combustion process continues.
6. If flame is not detected after first ignition trial, the ignition
control will repeat steps 3 and 4 four more times before
locking out the gas valve. The ignition control will then
automatically repeat steps 1 through 6 after 60 minutes.
7. To interrupt the 60 minute, move thermostat from “Heat”
to “OFF” then back to “Heat.” Heating sequence then
restarts at step 1.
Gas Pressure Adjustment
Gas Flow (Approximate)
Table 10
Furnace should operate at least 5 minutes before checking
gas flow. Determine time in seconds for two revolutions of
gas through the meter. (Two revolutions assures a more
accurate time.) Divide by two and compare to time in Table
10 below. If manifold pressure matches Table 12 and rate
is incorrect, check gas orifices for proper size and restriction.
Remove temporary gas meter if installed.
NOTE: To obtain accurate reading, shut off all other gas
appliances connected to meter.
Supply Pressure Measurement
A threaded plug on the inlet side of the gas valve provides
access to the supply pressure tap. Remove the threaded
plug, install a field provided barbed fitting and connect a
manometer to measure supply pressure. See Table 12 for
proper line pressure. Replace the threaded plug after
measurements have been taken.
Manifold Pressure Measurement
1. Remove the threaded plug from the outlet side of the
gas valve and install a field provided barbed fitting.
Connect to a manometer to measure manifold pressure.
2. Start unit and allow 5 minutes for unit to reach steady
state.
3. While waiting for the unit to stabilize, observe the flame.
Flame should be stable and should not lift from burner.
Natural gas should burn blue.
4. After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in Table
12.
NOTE: Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Take care to remove
barbed fitting and replace threaded plug.
Proper Combustion
Furnace should operate a minimum 15 minutes with correct
manifold pressure and gas flow rate before checking
combustion. Take combustion sample beyond the flue out
let and compare to the tables below. The maximum carbon
monoxide reading should not exceed 50 ppm.
Table 11
INTEGRATED IGNITION CONTROL
Blower on time will be 45 seconds after gas valve is energized. Blower off time will depend on “OFF TIME” Setting.
Figure 36