Lennox DAVE SIGNATURE SL297UHNV Installation Instructions Manual page 48

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 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 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
("WATCHGUARD" flame 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 20
GAS METER CLOCKING CHART
Seconds For One Revolution
SL297
Natural
Model
1 cu ft
Dial
90
-040
-060 60
-080 45
Natural-1000 btu/cu ft Propane 2500 btu/cu ft
LP/Propanae
2 cu ft 1 cu ft 2 cu ft
Dial Dial Dial
180 n/a n/a
120 150 300
90 112 224
Furnace should operate at least 5 minutes before check-
ing gas flow. 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 20. If manifold pressure matches table 21 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 thread-
ed plug, install a field-provided barbed fitting and connect
a manometer to measure supply pressure. Replace the
threaded plug after measurements have been taken.
Manifold Pressure Measurement
To correctly measure manifold pressure, follow the steps
below:
1 - Remove the threaded plug from the outlet side of
the gas valve and install a field-provided barbed
fitting. Connect measuring device "+" connection to
barbed fitting to measure manifold pressure.
2 - Start unit on low heat and allow 5 minutes for unit to
reach steady state.
3 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in
Table 21.
4 - Repeat on high heat.
5 - 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.
6 - Start unit and perform leak check. Seal leaks if found.
Manifold and Supply Line in w.g. and LP Conversion Kit
Model Fuel
Low
Fire
All Nat 1.7
-040
-060 LP 1.6
-080
Page 48
TABLE 21
Manifold Supply
Pressure Pressure
High
Min Max
Fire
3.5 4.5 10.5
4.0 11.0 13.0
Propane Kit
0-4500 ft
(0-1372m)
n/a
19K05
19K06