508297-01
Page 47 of 57
Issue 2219
5. Is the filter dirty or plugged? Dirty or plugged filters will
cause the limit control to shut the unit off.
6. Is gas turned on at the meter?
7. Is the manual main shut–off valve open?
8. Is the internal manual shut–off valve open?
9. Is the unit ignition system in lockout? If the unit locks
out again, inspect the unit for blockages.
Heating Sequence Of Operation
1. When thermostat calls for heat, combustion air inducer
starts.
2. Combustion air pressure switch proves blower
operation. Switch is factory set and requires no
adjustment.
3. After a 15 second pre-purge, 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. To interrupt the 60 minute period,
move thermostat from “Heat” to “OFF” then back to
“Heat”. Heating sequence then restarts at step 1.
Gas Pressure Adjustment
Gas Flow (Approximate)
Gas Meter Clocking Chart
Capacity
Seconds for One Revolution
Natural
LP
1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
Dial
030
120
240
300
600
045
80
160
200
400
070
55
110
136
272
090
41
82
102
204
110
33
66
82
164
135
27
54
68
136
Natural-1000 btu/cu ft LP-2500 btu/cu ft
Table 13. Gas Meter Clocking Chart
Supply Pressure Measurement
When testing supply gas pressure, use the 1/8” N.P.T.
plugged tap or pressure post located on the gas valve to
facilitate test gauge connection. See Figure 70. Check
gas line pressure with unit firing at maximum rate. Low
pressure may result in erratic operation or underfire. High
pressure can result in permanent damage to gas valve or
overfire.
On multiple unit installations, each unit should be checked
separately, with and without other units operating. Supply
pressure must fall within range listed in Table 15.
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
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 minimum 15 minutes with correct
manifold pressure and gas flow rate before checking
combustion. Take combustion sample beyond the flue
outlet and compare to the tables below.
Table 14.
Capacity
CO
2
% for Nat
CO
2
% for L.P.
All
7.5 - 8.5
8.2 - 9.5
The maximum carbon monoxide reading should not exceed
100 ppm.
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
13. If manifold pressure matches Table 15 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.