Verifying Burner Operation; Verifying Operation Of The Supply Air Limit Switch; Description Of Components - Nordyne M2RC-080 Installation Instructions Manual

registers and duct dampers to the desired
position and run the furnace for fifteen minutes
before taking any temperature readings. The
temperature rise is the difference between the
supply and return air temperatures.
For typical duct systems, the temperature rise
will fall within the range specified on the rating
plate with the blower speed at the factory
recommended setting. If the temperature rise
measured is outside the range specified, it may
be necessary to change the blower speed.
Lower blower speeds will increase the tem-
perature rise and higher blower speeds will
decrease the temperature rise.
The furnace is equipped with a multispeed
motor. Heating and cooling speed selection is
made by moving the leads on the integrated
control board located in the furnace. The wiring
diagram on the furnace and Figure 28 showthe
speed taps for adjusting motor speed.
If it is desired that the blower operate at the
same speed for heating and cooling, tape off
the terminal of the unused blower wire. Install
the jumper wire, found in the plastic instruction
bag, across the HEAT and COOL taps on the
control board. Reconnect the desired blower
tap to the piggyback quick connect.
The blower control is designed to start the
circulating air blower 30 seconds after the gas
valve is opened. The blower control is factory
wired to turn the blower motor off 120 seconds
after the gas valve is closed. This timing can be
changed using the BLOWER OFF timing switch
opposite the terminal block on the control board
(See Figure 28).
Verifying Burner Operation
To verify operation of the burners, make sure
that the blower compartment door is in place
and that there is power to the furnace. Set the
thermostat above room temperature and ob-
serve the ignition sequence. The flame can be
observed through the small clear window on
the burner box. The burner flame should carry
over between all burners. The flames should
be blue, without yellow tips. Flames should
extend from each burner without lifting, curling,
or floating. After veri_ing ignition, set the ther-
mostat below room temperature and verify that
the burner flame extinguishes completely.
Verifying Operation of the Supply Air
Limit Switch
To verify operation of the supply air limit switch,
make surethatthe blower dooris in place and that
28
there is power to the furnace. Completely block
the retum airflow to the furnace by installinga
close-of[ plate in place of or upstream of the
filter(s). Set the thermostat above room tem-
perature and verify that the Sequence of Opera-
tion is as described in these instructions. The
supply air limit switch should function to turn off
the gas valve within approximately five minutes.
The circulating air and combustion blowers
should continue to run when the supply air limit
switch opens. Remove the close-off plate imme-
diately after the supply air limit switch opens. If
the furnace operates for more than five minutes
with no return air, set the thermostat below room
temperature, shut off the power to the furnace,
and replace the supply air limit switch.
DESCRIPTION OF COMPONENTS
Figure 31 shows the location of each of the
functional components described below. If
any component of the furnace must be re-
placed, use only factory authorized replace-
ment parts. Contact your distributor for the
approved replacement parts.
Flame Sensor - The flame sensor acts to
prove that flame has carried over from the
igniter to the opposite end burner. If no flame
is sensed, the furnace will be shut down
automatically.
Gas Valve - The gas valve controls the flow
of gas to the burners. When the gas valve is
energized it automatically opens and regu-
lates the gas pressure in the manifold.
Pressure Switch - The pressure switch veri-
fies that the inducer is drawing the combustion
gases through the heat exchanger. It also
senses a blocked condensate drain condition.
Vent Pressure Switch (Downflow models
only) - The vent pressure switch reacts to
blockage in the vent or combustion air piping.
Supply Air Limit Switch - The supply air limit
switch prevents the air temperature leaving
the furnace from exceeding the maximum
outlet air temperature.
Vent Safety Switch - The vent safety switch
shuts the furnace down if the outlet flue gas
temperature increases above 160°F, This
switch protects the plastic flue system and the
inducer from over-temperature conditions.