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4 - Move gas valve switch to OFF.
5 - Replace the upper access panel.
Failure To Operate
If the unit fails to operate, check the following:
1 - Is the thermostat calling for heat?
2 - Are access panels securely in place?
3 - Is the main disconnect switch closed?
4 - Is there a blown fuse or tripped breaker?
5 - Is the lter dirty or plugged? Dirty or plugged lters
will cause the limit control to shut the unit o.
6 - Is gas turned on at the meter?
7 - Is the manual main shut-o valve open?
8 - Is the internal manual shut-o 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 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, ame sensor proves the ame, and
the combustion process continues.
6 - If ame is not detected after rst ignition trial, the
ignition control will repeat steps 3 and 4 four
more times before locking out the gas valve
(“WATCHGUARD” ame failure mode). The ignition
control will then automatically repeat steps 1 through
6 after 60 minutes. To interrupt the 60-minute
“WATCHGUARD” period, move thermostat from
“Heat” to “OFF” then back to “Heat”. Heating
sequence then restarts at step 1.
Gas Pressure Adjustment
Gas Flow (Approximate)
TABLE 11
GAS METER CLOCKING CHART
ML193
Unit
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
Natural-1000 btu/cu ft LP-2500 btu/cu ft
Furnace should operate at least 5 minutes before check-
ing gas ow. Determine time in seconds for two revolu-
tions of gas through the meter. (Two revolutions assures
a more accurate time.) Divide by two and compare to time
in TABLE 11. If manifold pressure matches TABLE 12 and
rate is incorrect, check gas orices for proper size and
restriction. Remove temporary gas meter if installed.
NOTE - To obtain accurate reading, shut o all other gas
appliances connected to meter.
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 61. Check
gas line pressure with unit ring at maximum rate. Low
pressure may result in erratic operation or underre. High
pressure can result in permanent damage to gas valve or
overre.
On multiple unit installations, each unit should be checked
separately, with and without units operating. Supply pres-
sure must fall within range listed in TABLE 12.
Manifold Pressure Measurement
1 - Connect the test gauge positive side “+“ to manifold
pressure tap on gas valve.
2 - Tee into the gas valve regulator vent hose and
connect to test gauge negative “-”.
3 - Start unit and let run for 5 minutes to allow for steady
state conditions.
4 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in
TABLE 12.
5 - Shut unit o and remove manometer as soon as an
accurate reading has been obtained. Take care to
replace pressure tap plug.
6 - Start unit and perform leak check. Seal leaks if found.
TABLE 12
Supply Line and Manifold Pressure (inches w.c.)
Unit Fuel
Manifold
Pressure
Line Pressure
All Nat. Gas 3.5 4.5 - 10.5
All L.P. Gas 10.0 11.0 - 13.0
NOTE - A natural to L.P. propane gas changeover kit is
necessary to convert this unit. Refer to the changeover kit
installation instruction for the conversion procedure.
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