Vi-Maintenance - Lennox LGM Series Manual

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 de­
mand.
4- When flame is established, compare reading to table
20. Do not bend electrodes.
5- Disconnect power to unit before disconnecting meter.
Make sure sensor wire is securely reconnected before
reconnecting power to unit.
TABLE 20
Nominal Signal
Manufacturer
Microamps
JOHNSON
NOTE-If the meter scale reads 0, the leads are re­
versed. Disconnect power and reconnect leads for
proper polarity.
10-Combustion Air Inducer
The combustion air inducer is factory set and is not field ad­
justable. However, operation should be monitored to en­
sure proper operation. The combustion air inducer is used
to draw fresh air into the combustion chamber while simul­
taneously expelling exhaust gases. The inducer operates
throughout the heating cycle.
On a heating demand, the ignition control is energized by
the A55 Unit Controller. The ignition control then allows 30
to 40 seconds for the combustion air inducer to vent ex­
haust gases from the burners. When the combustion air in­
ducer is purging the exhaust gases, the combustion air
prove switch is closing proving that the combustion air in­
ducer is operating before allowing the ignition control to en­
ergize. When the combustion air prove switch is closed and
the delay is over, the ignition control activates the first stage
operator of the gas valve (low fire), the spark and the flame
sensing electrode. Sparking stops immediately after flame
is sensed.
B-Cooling System Service Checks
LGM units are factory charged and require no further ad­
justment; however, charge should be checked periodically.
See section III- CHARGING.

VI-MAINTENANCE

A-Filters
LGM units use four 20 x 25 x 2" pleated throw-away type
filters. Filters may be accessed through the economizer /
filter access door. Filters should be checked monthly (or
more frequently in severe use) and cleaned or replaced
regularly. Take note of the "AIR FLOW DIRECTION" mark­
ing on the filter frame when re-installing.
Drop Out
0.5 - 1.0 .09
NOTE-Filters must be U.L.C. certified or equivalent for
use in Canada.
B-Lubrication
All motors and blower wheels used in LGM units are prelu­
bricated; no further lubrication is required.
C-Supply Air Blower Wheel
Annually inspect supply air blower wheel for accumulated
dirt or dust. Turn off power before attempting to remove ac­
cess panel or to clean blower wheel.
D-Evaporator Coil
Inspect and clean coil at beginning of each season. Clean
using mild detergent or commercial coil cleanser. Check
condensate drain pan and line, if necessary. Flush coil and
condensate drain with water taking care not to get insula­
tion, filters and return air ducts wet. Check connecting lines
and coil for evidence of oil and refrigerant leaks.
E-Condenser Coil
Clean condenser coil annually with water and inspect
monthly during the cooling season.
Clean the all-aluminum coil by spraying the coil steadily and
uniformly from top to bottom. Do not exceed 900 psi or a
45_ angle; nozzle must be at least 12 inches from the coil
face. Take care not to fracture the braze between the fins
and refrigerant tubes. Reduce pressure and work cautious­
ly to prevent damage.
Slab Coils -
Clean condenser coil annually with detergent or commer­
cial coil cleaner and inspect monthly during the cooling sea­
son. Check connecting lines and coil for evidence of oil and
refrigerant leaks.
NOTE-If owner complains of insufficient cooling, the
unit should be gauged and refrigerant charge checked.
Refer to Gauge Manifold Attachment and Charging sec­
tions in this manual.
F-Electrical
1- Check all wiring for loose connections.
2- Check for correct voltage at unit (unit operating).
3- Check amp-draw on both condenser fan motor and
blower motor.
Fan Motor Rating Plate ____ Actual ________
Indoor Blower Motor Rating Plate____ Actual____
4- Check crankcase heater temperatures to ensure they
are operating.
5- Check compressor sump thermistors to ensure they
are making contact with compressor shell (ultra high ef­
ficiency units only).
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