Page 49
9 − Replace the access panel.
10− Turn on all electrical power to to the unit.
11− Set the thermostat to desired setting.
NOTE
− When unit is initially started, steps 1 through 11
may need to be repeated to purge air from gas line.
12− If the appliance will not operate, follow the instructions
Turning Off Gas to Unit" and call the gas supplier.
Turning Off Gas to Unit
1 − Set the thermostat to the lowest setting.
2 − Turn off all electrical power to the unit if service is to be
performed.
3 − Remove the access panel.
4 − Move the gas valve switch to the
OFF
position.
5 − Replace the 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?
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 gas valve turned on?
9 − Is the unit ignition system in lock out? If the unit locks out
again, inspect the unit for blockages.
10 − Is blower harness connected to ignition control? Fur-
nace will not operate unless harness is connected.
Gas Pressure Measurement
Gas Flow (Approximate)
TABLE 24
GAS METER CLOCKING CHART
SLP98
Unit
Seconds for One Revolution
Natural
LP
1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dial
2 cu ft
DIAL
−70
55
110
136
272
−90
41
82
102
204
−110
33
66
82
164
−135
27
54
68
136
Natural−1000 btu/cu ft LP−2500 btu/cu ft
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 24 below. If manifold pressure matches table 28
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. Replace the
threaded plug after measurements have been taken.
Manifold Pressure Measurement (Figure 53)
To correctly measure manifold pressure, the differential
pressure between the positive gas manifold and the nega-
tive burner box must be considered.
Use pressure test
adapter kit (available as Lennox part 10L34) to assist in
measurement.
1 − Remove the threaded plug from the outlet side of the
gas valve and install a field−provided barbed fitting.
Connect measuring " connection to barbed
fitting to measure manifold pressure.
2 − Tee into the gas valve regulator vent hose and connect
measuring device −" connection.
3 − Start unit on low heat (35% rate) and allow 5 minutes
for unit to reach steady state.
4 − While waiting for the unit to stabilize, notice the flame.
Flame should be stable and should not lift from burner.
Natural gas should burn blue.
5 − After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
25.
6 − Repeat steps 3, 4 and 5 on high heat.
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.
CAUTION
Do not attempt to make adjustments to the gas valve.
Operating Pressure Signal (Delta P) Measurement
(Figure 54)
Operating pressure signal can be taken while the manifold
pressure pressure check is taken (using two measuring de-
vices). Or, taken after the manifold pressure measurement
is complete.
1 − Tee into the negative line between the gas valve and
pressure switch and connect to measuring device
negative −".
2 − Tee into the positive line between the gas valve and
pressure switch and connect to measuring device
po".
3 − Start unit on low heat (35% rate) and allow 5 minutes
for unit to reach steady state.
4 − After allowing unit to stabilize for 5 minutes, record op-
erating pressure signal and compare to value given in
table 25.
5 − Repeat steps 3 on 4 high heat.
