Clamshell Heat Exchanger; Flame Rollout Switches; Primary Limit Control; Backup Secondary Limit Control - Lennox G61MPV Service Manual

SureLight Board 49M59 Sensor
NORMAL FLAME SIGNAL > 0.23 MICROAMPS
LOW FLAME SIGNAL
DROP OUT SIGNAL
5/16"
FIGURE 14
SureLight Board 100870 Sensor
NORMAL FLAME SIGNAL > 1.50 MICROAMPS
LOW FLAME SIGNAL
DROP OUT SIGNAL
5/16"
FIGURE 15

8. Clamshell Heat Exchanger

G61MPV units use an aluminized steel primary and
stainless steel secondary heat exchanger assembly.
Heat is transferred to the air stream from all surfaces of
the heat exchanger. The shape of the heat exchanger en-
sures maximum efficiency.
The combustion air inducer pulls fresh air through the burn-
er box. This air is mixed with gas in the burner venturi and
at the corbel orifices. The gas / air mixture is then burned
at the entrance of each clamshell. Combustion gases are
then pulled through the primary and secondary heat exchang-
ers and exhausted out the exhaust vent pipe.
9. Flame Rollout Switches (S47)
Flame rollout switch S47 is a high temperature limit located
on each side of the burner box. Each furnace is equipped
with two identical switches. The limit is a N.C. SPST manu-
al-reset limit connected in series with the primary limit S10.
When S47 senses rollout, the circuit breaks and the ignition
control immediately stops ignition and closes the gas
valve.
< 0.22 MICROAMPS
= 0.16 MICROAMPS
< 1.40 MICROAMPS
= 0.20 MICROAMPS
Page 43
If unit is running and flame rollout is detected, the gas valve
will close and ignition control will be disabled. Rollout can
be caused by a blocked heat exchanger, flue or lack of
combustion air. The switch is factory set to trip (open) at
250°F and cannot be adjusted. The switch can be manually
reset. To manually reset a tripped switch, push the reset but-
ton located on the control.
10. Primary Limit Control (S10)
Figure 16 shows the primary limit (S10) used on G61MPV
units located in the heating vestibule panel. S10 is provided
with a shield on some models (figure 16) and must not be re-
moved. Note orientation of shield and limit if limit is replaced.
When excess heat is sensed in the heat exchanger, the limit
will open. Once the limit opens, the furnace control ener-
gizes the supply air blower and de−energizes the gas valve.
The limit automatically resets when unit temperature re-
turns to normal. The switch is factory set and cannot be ad-
justed.
11. Backup Secondary Limit Control (S113)
(G61MPV−090, 110, 135 only)
Backup secondary limit control S113 is a N.C. auto−reset
switch located on the combustion air inducer. S113 acts as
a backup to primary limit S10 in the event of an indoor blow-
er failure. S113 contacts open when temperature on the
CAI reaches 142°.
12. Gas Valve (GV1)
The G61MPV uses a two−stage gas valve manufactured by
Honeywell (figure 44) or White Rodgers (figure 45). The
valves are internally redundant to assure safety shut−off. If
the gas valve must be replaced, the same type valve must
be used.
24VAC terminals and gas control knob or switch are located
on the valve. All terminals on the gas valve are connected to
wires from the electronic ignition control. 24V applied to the ter-
minals energizes the valve.
Inlet and outlet pressure taps are located on the valve. A regu-
lator adjustment screw is located on the valve.
LPG change over kit s are available from Lennox. Kits include
burner orifices and a gas valve regulator conversion kit.
The burner box is sealed and operates under a negative
pressure. A pressure hose is connected from the burner
box to the gas valve. The gas valve senses the pressure in
the burner box and changes gas valve outlet (manifold)
pressure based on changes in the burner box pressure.
The intent is to compensate for different vent configura-
tions which can greatly affect the rate of the unit.