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3. After validating the flame, change the thermostat setting to
below room temperature.
4. Verify the burner flame is completely extinguished.
5. Replace the burner compartment door.
Verify 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 airflow to the furnace by installing a close-
off plate in place of or upstream of the filter(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
power to the furnace, and replace the limit switch.
HEATING VALUE BTU/CU. FT
ALTITUDE ABOVE
SEA LEVEL
800 TO 899 900 TO 999
ZERO TO 5,000
3.5
FT.
Table 3. Manifold Pressure Setting (In WC)
for Natural Gas
OPERATING SEQUENCE
The operating sequences for the heating, cooling, and fan
modes are described below. Refer to the field and unit wiring
diagram. See
Figure 12 (page 23)
Heating Cycle
1. The thermostat calls for heat by energizing the W terminal
with 24VAC.
2. The control verifies the safety circuit pressure switch is open
and high temperature limit switch circuit is closed.
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 control runs the inducer for a 30 second pre-purge.
5. The control energizes the igniter output for a 30 second
warm-up period.
6. The control energizes the main gas valve for 3 seconds.
7. If the flame is proved after igniting the gas, the control de-
energizes the igniter. The gas valve and inducer remain
energized. The control goes to blower on delay.
8. If flame is present, the control energizes the blower on
the selected HEAT speed 30 seconds after the gas valve
opened. The gas valve remains energized while the inducer
ramps to Max. RPM over a programmed time period.
9. When the thermostat demand for heat is satisfied, the control
de-energizes the gas valve. The inducer output remains on
for a 90 second post-purge period.
10. Blower off timing of 60, 90, 120, & 180 seconds (depending
on the movable jumper setting) begins when the thermostat
is satisfied. See Figure 14 (page 16). The control will
operate at the selected HEAT speed of 60 seconds, then
change to FAN speed for the remaining off delay time. 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.
ORIFICE
1,000 TO
1,100
FACTORY
3.5
3.5
INSTALLED
and
Figure 13 (page
24).
Cooling Cycle
1. The thermostat calls for cooling by energizing the Y & G
terminal with 24VAC.
2. The control energizes the blower in the cooling speed and
sends 24VAC to the contactor in the condensing section.
3. When the thermostat removes the call for cooling, the
contactor in the outdoor condensing section 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. See
11). The control defaults to MEDIUM HIGH if the movable
jumper is not attached.
• 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 and reset to delayed ON
timing.
• A call for fan is ignored while in lockout.
EQUIPMENT MAINTENANCE
WARNING:
ELECTRICAL SHOCK, FIRE OR
EXPLOSION HAZARD
Failure to follow safety warnings exactly could
result in serious injury, death, or property damage.
Improper servicing could result in dangerous
operation, serious injury, death or property
damage.
• Before servicing, disconnect all electrical power
to furnace.
• When servicing controls, label all wires prior to
disconnecting. Reconnect wires correctly.
• Verify proper operation after servicing.
CAUTION:
Use care when removing parts from this unit.
Personal injury can result from sharp metal edges
present in all equipment of sheet metal construction.
Proper maintenance is important to achieve optimum
performance from the system. The ability to properly perform
maintenance on this equipment requires certain mechanical
skills and tools. If you do not possess these skills, contact your
dealer for maintenance. Consult your local dealer about the
availability of maintenance contracts. Routine maintenance
should include the following:
CAUTION:
The unit should never be operated without a filter
in the return air system. Replace disposable filters
with the same type and size.
Figure 6 (Page
15
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