Start-Up; Preliminary And Seasonal Checks; Heating Start-Up; Safety Or Emergency Shutdown - Lennox G24M SERIES Unit Information

The switch is a single-pole single-throw pressure
switch electrically connected to the furnace control.
The purpose of the switch is to prevent burner opera-
tion if the combustion air blower is not operating.
PROVE SWITCH
COMBUSTION AIR BLOWER
PROVE SWITCH
Normally Open
Closes on Negative Pressure
PROVE
SWITCH
FIGURE 19
On start-up, the switch senses that the combustion air
blower is operating. It closes a circuit to the furnace
control when pressure inside the combustion air
blower increases above switch setting (negative) w.c.
The pressure sensed by the switch is relative to atmo-
spheric pressure. If the flue becomes obstructed dur-
ing operation, the switch senses a loss of negative
pressure (pressure becomes more equal with atmo-
spheric pressure) and opens the circuit to the furnace
control and gas valve. The switch trip pressure is dif-
ferent depending on unit model number. The trip pres-
sure is printed on the side of the limit.
The switch is factory set and is not field adjustable. It is
a safety shut-down control in the furnace and must not
be bypassed for any reason.
II--PLACEMENT AND INSTALLATION
Make sure unit is installed in accordance with installa-
tion instructions and applicable codes.
Sensing Tube
Attaches to Top
Side Of Blower
Top
Back
Right
Left
Front
Bottom
Page 16
III--START-UP
A--Preliminary and Seasonal Checks
1 - - Inspect electrical wiring, both field and factory
installed for loose connections. Tighten as required.
2 - - Check voltage at disconnect switch. Voltage must
be within range listed on the nameplate. If not,
consult the power company and have voltage
condition corrected before starting unit.
B--Heating Start-Up
1 - - Set thermostat to OFF position. Close manual
knob on gas valve.
2 - - Wait 5 minutes.
3 - - Open manual knob on gas valve, replace burner
access door and turn on unit electrical supply.
WARNING
Shock and burn hazard.
G24M units are equipped with either a direct spark
or hot surface ignition system. Do not attempt to
light manually.
4 - - Set fan switch to AUTO or ON and move system
selection switch to HEAT. Adjust thermostat to a
setting above room temperature.
5 - - If unit does not light the first time, the SureLight
control will attempt four more ignitions, the Ram
control will attempt two more ignitions before
locking out.
6 - - If lockout occurs, repeat steps 1, 2, 3 and 4.
C--Safety or Emergency Shutdown
Turn off unit power. Close manual and main gas valves.
IMPORTANT
In case emergency shutdown is required, turn off
the main shut-off valve and disconnect the main
power to unit. These controls should be properly
labeled by the installer.
D--Extended Period Shutdown
Turn off thermostat or set to “UNOCCUPIED” mode.
Close all gas valves (both internal and external to unit)
to guarantee no gas leak into combustion chamber.
Turn off power to unit. All access panels, covers and
vent caps must be in place and secured.