Lennox LGT Series Unit Information page 37

5-Proper Gas Flow
To check for proper gas flow to burners, determine Btuh
input from unit rating plate or the gas heating capacity in
the SPECIFICATIONS tables. Divide this input rating by
the Btuh per cubic foot of available gas. Result is the num-
ber of cubic feet per hour required. Determine the flow of
gas through gas meter for two minutes and multiply by 30
to get hourly flow of gas to the burners.
NOTE - To obtain accurate reading, shut off all other gas
appliances connected to meter.
6-Inshot Burner
Burners are factory set for maximum air and cannot be
adjusted. Always operate unit with access panel in place.
A peep hole is furnished in the heating access panel for
flame viewing. Natural gas should burn basically blue with
some clear streaks. L.P. gas should burn mostly blue with
some clear yellow streaks.
Follow steps below to remove burner assembly.
1 - Turn off power to unit and shut off gas supply.
2 - Remove screws holding the burner support cap.
3 - Burner assembly is a cluster assembly (figure 31)
and can be removed as one.
4 - Clean and reassemble (reverse steps 1-3).
5 - Be sure to secure all wires and check plumbing.
6 - Turn on power to unit. Follow lighting instructions
attached to unit and operate unit in heating mode.
Check burner flames. They should be blue with
yellow streaks.
TYPICAL GAS BURNER ASSEMBLY
BURNERS
(Typical)
BURNER
SUPPORT
ORIFICE
FIGURE 26
7-Spark Electrode Gap
The spark electrode assembly can be removed for inspec-
tion by removing two screws securing the electrode as-
sembly and sliding it out of unit.
For proper unit operation, electrodes must be positioned
and the spark gap set correctly.Spark gap may be checked
with appropriately sized twist drills or feeler gauges.
BURNER
SUPPORT CAP
SENSOR
Disconnect power to the unit and remove electrode as-
sembly. The gap should be between 0.125" + 0.015" (3.2
mm + .4 mm). See figure 21.
8-Heat Exchanger
To Access or Remove Heat Exchanger From Unit:
1 - Turn off gas and electric power.
2 - Remove access panel(s) and unit center mullion.
3 - Remove gas valve, manifold assembly and burners.
4 - Remove combustion air inducer and flue box. Pay
careful attention to the order in which gaskets and
orifice are removed.
5 - Support heat exchanger (to prevent it from falling
when final screws are removed.)
6 - Remove screws supporting heat exchanger.
7 - To install heat exchanger, reverse procedure. Be
sure to secure all wires and check plumbing and
burner plate for airtight seal. Screws must be
torqued to 35 in.- lbs. to ensure proper operation.
9-Flame Sensing
Flame current is an electrical current which passes from
the ignition control through the sensor electrode during
unit operation.
The current passes from the sensor through the flame to
the ground electrode (located on the flame electrode) to
complete a safety circuit. The electrodes should be locat-
ed so the tips are at least 1/2" (12.7 mm) inside the flame
envelope. Do not bend electrodes. To measure flame cur-
rent, follow the procedure on the following page:
NOTE-Electrodes are not field adjustable. Any alterations
to the electrode may create a hazardous condition that
can cause property or personal injury.
1 - Disconnect power to unit.
2 - Remove lead from sensing electrode and install
a 0-50DC microamp meter in series between the
sensing electrode and the sensing lead.
3 - Reconnect power and adjust thermostat for heating
demand.
4 - When flame is established, compare reading to
table 12. Do not bend electrodes.
5 - Disconnect power to unit before disconnecting
meter. Make sure sensor wire is securely
reconnected before reconnecting power to unit.
Manufacturer
Johnson
NOTE-If the meter scale reads 0, the leads are reversed.
Disconnect power and reconnect leads for proper polarity.
Page 37
TABLE 12
Nominal Signal
Drop Out
Microamps
0.5 - 1.0 .09