Lennox ELITE 12GCS Series Unit Information page 12

7−Clamshell Heat Exchanger
The 12GCS units use an aluminized steel tapered S−curve
heat exchanger. Heat is transferred to the air stream from all
surfaces of the heat exchanger. The combustion air inducer
blower pulls fresh air through the burner box. This air is mixed
with gas in the burner Venturi. The gas/air mixture is then
burned at the entrance of each clam shell. Combustion gases
are then pulled through the heat exchanger and exhausted out
the vent.
12GCS−1 MODEL BURNER ASSEMBLY
ELECTRODE/SENSOR
FIGURE 10
8−Burners/Orifices
All 12GCS units use inshot burners. A flame retention ring lo-
cated in the burner end keeps flame from lifting off the burner.
All 12GCS units use orifices that are precisely matched to the
burner's input (see figure 10 for burner box assembly.) Each
burner is supported by the orifice but can easily be removed for
service. If service is necessary, the following instructions apply.
1. Close main manual shut−off valve and shut off all power
to the unit.
2. Open the union fitting in the gas supply line just up-
stream of the unit gas valve and downstream from the
manual shut−off valve.
3. Remove the four screws, two on the side and two on the
bottom, that mount the burner rack assembly to the
burner plate.
4. Disconnect wiring to the gas valve and the electrode/
flame sensor. Remove the burner rack assembly from
the unit by pulling back. Burners and gas orifices are
now accessible to service.
5. Reverse the above procedure to replace the assembly.
Make sure that burners are level and centered into
each burner's corresponding heat exchanger tube.
1/8" SPARK GAP
Page 12
9−Electrode/Flame Sensor
The electrode/sensor is used for ignition and is located in the
left hand mounting hole. 12GCS −1 models will have a single
electrode/sensor on the same bracket (see figure 10).
12GCS−2 models will have a split electrode/sensor. See figure
11. The spark gap is 1/8" and is the same for both type elec-
trodes used. The electrode tip protrudes into the flame enve-
lope of the adjacent burner. If the blower/ignition control A3
does not receive signal from the electrode/flame sensor indi-
cating that the burners have established flame, the main gas
valve GV1 will close after the 10−second sensing interval built
into the ignition A3. To measure flame current follow the proce-
dure below:
1− Disconnect power to unit.
2− Remove lead from sensing electrode and install a micro-
amp meter in series between the sensing electrode and
sensing lead.
3− Reconnect power and adjust thermostat for heating de-
mand.
4− When flame is established, meter reading should be
between 1 and 5 microamps. Drop−out signal is .45
amps.
5− Disconnect power to unit before disconnecting meter.
Make sure sensor wire is securely reconnected before
reconnecting power to unit.
12GCS−2 MODEL BURNER ASSEMBLY
FIGURE 11
C−Evaporator Blower B3 and Capacitor C4
All 12GCS and 12CHP model units use single−phase motors.
A single run permanent split capacitor is mounted on the blow-
er housing. See wiring diagram for factory−set speed tap. See
SPECIFICATIONS and ELECTRICAL DATA sections
more information. See motor nameplate for capacitor ratings.
SENSOR
ELECTRODE
for