Lennox ELITE 12GCS Series Unit Information page 11

DEFROST CONTROL DEFROST TEST CYCLE TIME
T1−30 minutes
T2−60 minutes
T3−90 minutes
After test pins are jumpered and appropriate cycle time has
elapsed, the reversing valve should shift to defrost mode
and outdoor fan should stop. After 2 seconds of defrost op-
eration, reversing valve should shift back to heating opera-
tion and outdoor fan should start.
B−Gas Components (GCS Only)
1−Primary Limit S10
All 12GCS units are equipped with a closed face, auto reset,
high temperature limit. S10 protects the unit from high temper-
ature operation. It is located on the heating vest panel just be-
low the burner box. The N.C. contacts are actuated by a bi−
metal shim when temperature in the heating compartment is
high enough. When the N.C. contacts open, the ignition control
and gas valve are de−energized shutting down the unit except
for the main blower. The limit will automatically reset when unit
temperature returns to normal. All limits are 3" in length with
varying setpoints. Limit setpoints will be printed on side of
switch.
IMPORTANT
Limit replacement must be of exact length and set-
point. Different length or setpoint can result in un-
safe operation of unit.
2−Rollout Switch S47
Rollout switch S47 is a high temperature limit located on the
burner box. The switch is a N.C. manual reset switch con-
nected in series with limit S10 and ignition control A3. When
S47 senses flame rollout (opens), ignition control and gas
valve are de−energized. The switch is factory set at 400_ F and
cannot be adjusted. S47 can be manually reset when tempera-
tures allow.
3− Secondary Limit S21
S21 is a high temperature limit located on the blower scroll (see
figure 8). The switch is an automatic reset disc with a bi−metal
shim that actuates on temperature rise. S21 is wired in series
with primary limit S10. When the N.C. contacts open the igni-
tion control and gas valve are de−energized. The switch is a
safety feature should the circulating blower B3 fail. The switch
will automatically reset when temperatures in the blower hous-
ing return to normal. Limit setpoints will be printed on side of
switch.
FIGURE 8
7 seconds
14 seconds
21 seconds
S21
4−Combustion Air Prove Switch S18
The combustion air prove switch S18 is a SPST N.O. differen-
tial prove switch, used to monitor combustion air inducer blow-
er operation. The switch is wired in series with limit S21 and
ignition board A3. When the combustion air inducer begins op-
eration and pressure drop reaches .17"wc. across the switch,
the contacts close and ignition can be initiated.
5−Combustion Air Inducer B6
Combustion air inducer B6 provides fresh air to the burners
while clearing the heat exchanger of exhaust gases. The in-
ducer begins operating immediately upon receiving a thermo-
stat demand (provided switch is open and not by−passed) and
is de−energized immediately when thermostat demand is satis-
fied. All combustion air inducer motors are sealed and cannot
be oiled.
6−Gas Valve GV1
The 12GCS uses a gas valve manufactured by Honeywell.
The valves are internally redundant to assure safety shutoff. If
the valve must be replaced, the same valve type must be used.
For natural gas units, line pressure should be 7.0"w.c. and
manifold pressure should be 3.5" w.c. For LP units, line pres-
sure should be 11.0"w.c. and manifold pressure should be
10.0" w.c.
24VAC terminals and gas control knob are located on top of the
valve. All terminals on the gas valve are connected by wires to
the ignition board A3. 24VAC applied to the "MV"on the valve
opens the valve. A regulator adjustment screw is located on the
valve. See figure 9 .
An LP changeover kit (Lennox part #42K91) is available. The
kit includes burner orifices and a regulator conversion kit. Fol-
low kit instructions when converting unit to LP.
TYPICAL ACCESS TO REGULATOR
FOR ADJUSTMENT AND L.P. CHANGEOVER
INLET
PRESSURE
TAP
PRESSURE
REGULATOR
ADJUSTING
SCREW
(White)
Page 11
OUTLET
PRESSURE
TAP
ON
GAS VALVE
SHOWN IN OFF
OFF
POSITION
CAP SCREW (Black)
SPRING Tapered End
Down (Red)
INLET
PRESSURE
TAP
GAS INLET
FIGURE 9