Lennox LGH094U Unit Information page 58

5-Proper Gas Flow
To check for proper gas flow to burners, determine Btuh in­
put 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 number 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 ad­
justed. 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.
Figure 39 shows how to remove burner assembly.
1- Turn off power to unit and shut off gas supply.
2- Remove screws holding the burner support cap.
3- Slide each burner off its orifice.
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
BURN­
ERS
BURNER
SUPPORT
ORIFICE
FIGURE 39
7-Spark Electrode Gap
The spark electrode assembly can be removed for inspection
by removing two screws securing the electrode assembly 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. Disconnect power to the unit and remove
electrode assembly. The gap should be between 0.125" +
0.015" (3.2 mm + .4 mm). See figure 32.
BURNER
SUPPORT CAP
SENSOR
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 ori­
fice are removed.
5- Support heat exchanger (to prevent it from falling when fi­
nal 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 en­
sure proper operation.
9-Flame Sensing
Flame current is an electrical current which passes from the
ignition control through the sensor electrode during unit op­
eration. The current passes from the sensor through the
flame to the ground electrode (located on the flame elec­
trode) to complete a safety circuit. The electrodes should
be located so the tips are at least 1/2" (12.7 mm) inside the
flame envelope. Do not bend electrodes. To measure flame
current, follow the procedure on the following page:
NOTE-Electrodes are not field adjustable. Any alter­
ations to the electrode may create a hazardous con­
dition 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 25.
Do not bend electrodes.
5- Disconnect power to unit before disconnecting meter.
Make sure sensor wire is securely reconnected be­
fore reconnecting power to unit.
Manufacturer
JOHNSON
NOTE-If the meter scale reads 0, the leads are re­
versed. Disconnect power and reconnect leads for
proper polarity.
Page 58
TABLE 25
Nominal Signal
Drop Out
Microamps
0.5 - 1.0 .09