Surelight Control Self Check - Lennox G61MPV Service Manual

B−SureLight Board 49M59
Sequence depends on type thermostat used.
G61MPV units are applicable for single stage or two
stage thermostats. Both type thermostats are de-
scribed below. Thermostat jumper E20 dictates which
mode unit will operate in. See flow chart for more se-
quence detail.

SureLight Control Self Check

When there is a call for heat, the SureLight® integrated
control runs a self check. The control checks for S10 prima-
ry limit, S21 secondary limit (s) and S47 rollout switch nor-
mally closed contacts. The control also checks for S102
high heat and S128 low heat prove switch normally open
contacts. Once self check is complete and all safety
switches are operational, heat call can continue.
Two−Stage Thermostat, Two−Stage Heat. Jumper E20
set at TWO".
1− SureLight control energizes combustion air inducer B6
on low heat speed. Combustion air inducer runs until
S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
2− SureLight control begins 20 second ignitor warm up
period.
3− Gas valve opens on first−stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
4− Flame is sensed, gas valve remains on first−stage
heat, ignitor de−energizes.
5− After 45 second delay, indoor blower B3 is energized
on low heat speed.
The furnace will stay in this mode until first−stage de-
mand is satified OR a second−stage heat demand is
initiated.
6− Second−stage heat demand initiated. A 30 second
second−stage recognition period begins.
7− The combustion air inducer ramps up to high heat
speed.
8− S102 high heat prove switch closes and the gas valve
energizes second stage heat.
9− B3 indoor blower ramps up to high heat speed.
Single−Stage Thermostat, Two−Stage Heat. Jumper
E20 set at SINGLE"
1− SureLight control energizes combustion air inducer B6
on low heat speed. Combustion air inducer runs until
S128 low heat prove switch contacts close (switch
must close within 2 1/2 minutes or control goes into
Watchguard Pressure Switch mode. High heat prove
switch S102 may also close). A 15 second pre−purge
follows once S128 closes.
2− SureLight control begins 20 second ignitor warm up
period.
3− Gas valve opens on first stage for a 4 second trial for
ignition. Ignitor stays energized during the trial or until
flame sensed.
4− Flame is sensed, gas valve remains on first−stage
heat, ignitor de−energizes.
5− After 45 second delay, indoor blower B3 is energized
on low heat speed.
6− A 10 minute (factory set) or 15 minute (field set) sec-
ond−stage heat delay period begins.
7− After the delay the combustion air inducer ramps up to
high heat speed.
8− S102 high heat prove switch closes and the gas valve
energizes second−stage heat.
9− B3 indoor blower ramps up to high heat speed.
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