Lennox MPGA 050 B3, Application Manual

STARTUP AND OPERATIONAL CHECKOUT

Do not use this furnace as a construction heater.
Use of this furnace as a construction heater
exposes the furnace to abnormal conditions,
contaminated combustion air and the lack of air
filters. Failure to follow this warning can lead to
premature furnace failure and/or vent failure which
could result in a fire hazard and/or bodily harm.

The automatic gas valve controls the flow of gas to

the main burners. The ignition system control switch built
into the automatic valve body has 2 positions: "OFF" and
"ON" (Figure 13). To shut off gas manually:

Rotate

 switch

from "ON" to "OFF" position. When in "OFF" position, the
main burners are extinguished.

This furnace is equipped with an automatic hot-

surface ignition control and does not require the manual
lighting for furnace operation.

Figure 13

GAS CONTROL DIAGRAM

Do not attempt to manually light the burners.
Failure to follow this warning can lead to electrical
shock that could result in bodily harm.

After the ductwork connections have been made, gas

piping and electrical wiring completed and the furnace
has been properly vented, the unit should be started and
adjusted for proper operation. Check off the following
steps as they are completed.

1. Be sure all electrical power is OFF.
2. Check all wiring using proper wiring diagram on

inside of the control box cover.

3. Turn ON the electrical power.
4. Set the 

gas control knob 

in the "ON"

 position.

5. Set the thermostat above room temperature.
6. The 

ignitor will spark and the main burner

 will ignite.

Figure 14

TYPICAL FLAME APPEARANCE

(Main Burners)

7. Recheck for leaks in the manual shut off valve, gas

control valve and gas connections using a soap
solution.

Never use an open flame when testing for gas
leaks! Use of an open flame could lead to a fire or
explosion.

Many soaps used for leak testing are corrosive to
certain metals. Piping must be rinsed thoroughly
with clean water after leak check has been
completed.

Manifold  Pressure  Adjustment:

Turn OFF the gas and electrical before

preceeding!

 Remove the manifold pressure tap pipe

plug from the gas valve (Figure 13 outlet pressure tap)
and install a pressure tap and connect it to a manometer.
Turn on the gas and electrical supplies, then measure the
manifold pressure 

with the furnace in operation.

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