Verifying Operation Of The Supply Air Limit Switch; Operating Sequence; Heating Cycle; Cooling Cycle - Nordyne M4RC Upflow Installation Instructions Manual

NOTE: The fl ame should carry over immediately
between all burners without lifting off, curling, or fl oating.
The fl ames should be blue, without yellow tips.
3. After validating the fl ame, change thermostat setting
to below room temperature.
4. Verify the burner fl ame is completely extinguished.
5. Replace the burner compartment door.

Verifying Operation of the Supply Air Limit Switch

A properly functioning limit switch should turn off the gas
valve when the return is blocked (time depends on how
well the return air is blocked). The circulating air and
combustion blowers should continue to run when the
limit switch opens.
1. Verify the blower door is securely mounted in place
and that there is power to the furnace.
2. Block the return airfl ow to the furnace by installing a
close-off plate in place of or upstream of the fi lter(s).
3. Set the thermostat above room temperature and
observe the Operating Sequence.
4. Remove the close-off immediately after the limit switch
opens. If the furnace continues to operate with no
return air, set the thermostat below room temperature,
shut off the power to the furnace, and replace the limit
switch.

OPERATING SEQUENCE

The operating sequences for the heating, cooling,
and fan modes are described below. Refer to the fi eld
and furnace wiring diagrams: (Figures 37, page 29),
(Figure & 38, page 30) and (Figure 40, page 39).

Heating Cycle

1. The thermostat calls for heat by energizing the W
terminal with 24VAC.
2. The control verifi es the pressure switch is open.
3. If the pressure switch is open, the control energizes
the inducer and waits for the pressure switch to close.
The pressure switch must close within 10 seconds.
4. The inducer runs for a 30 second pre-purge.
5. The control energizes the Hot Surface Igniter (HSI)
output for the appropriate warm-up time limit.
6. The main gas valve energizes for 3 seconds.
7. If the fl ame proved and ignites the gas, the control de-
energizes the HSI. The gas valve and inducer remains
energized. The control goes to blower on delay.
8. If fl ame is present, the control energizes the blower
on the selected HEAT speed 30 seconds after the
gas valve opened. The gas valve and inducer remain
energized.
9. When the thermostat demand for heat is satisfi ed, the
control de-energizes the gas valve. The Inducer output
remains on for a 30 second post-purge period.
32
10. Blower off timing begins when the thermostat is
satisfi ed. The control will operate at the selected HEAT
speed of 60, 90, 120, or 180 seconds. If the blower
off delay jumper is not present, the fan should still
operate for 120 seconds at the selected HEAT speed.
The Indoor blower motor is de-energized after a blower
off delay as selected by the movable jumper.

Cooling Cycle

1. The thermostat calls for cooling by energizing the G
and Y terminals with 24VAC.
2. The control energizes the blower in cooling speed and
sends 24VAC to the contactor in the condensing unit.
3. When the thermostat removes the call for cooling,
the contactor in the outdoor condensing unit is de-
energized and the control continues to run the fan for
a period of 60 seconds.

Fan Mode

• When the thermostat energizes the G terminal for
continuous fan (without calling for heat or cooling), the
indoor fan is energized on the selected FAN speed.
• If a call for cooling occurs during continuous fan, the
blower will switch over to the selected COOL speed.
• If the W terminal receives a call for heat during
continuous fan, the blower will de energize.
• A call for fan is ignored while in lockout.

MAINTENANCE

WARNING:
These maintenance instructions are primarily
intended to assist qualified technicians
experienced in the proper maintenance and
operation of this appliance.
Proper maintenance is most important to achieve the best
performance from a furnace. Follow these instructions for
years of safe, trouble free operation.
• Always replace the doors on the furnace after servicing
or cleaning/changing the fi lters. Do not operate the
furnace without all doors and covers in place.
• Verify the thermostat is properly installed and will
not be affected by drafts or heat from lamps or other
appliances.
• To achieve the best performance and minimize
equipment failure it is recommended that a yearly
maintenance checkup be performed. At a minimum,
this check should include the following items: