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5.
If second-stage heat is required, the thermostat
second stage heat contacts close and send a signal
to the integrated control. The integrated control either
increases the firing rate to 70 percent (if the current
rate is at or below 60 percent) or increases the
firing rate by 10 percent (if the current rate is above
60 percent). If the call for heat continues 5 minutes
beyond this initial upstage, the rate will be increased
by 10 percent every 5 minutes until the call for heat is
satisfied or the furnace reaches 100 percent rate. As
the firing rate increases, the indoor blower motor is
adjusted to a speed which is appropriate for the target
rate.
6.
If second-stage heat demand is satisfied, but first stage
is still present, the furnace will continue to operate at
the present firing rate until the heat cycle ends.
7.
When the demand for first and second stage heat
is satisfied, the gas valve is de-energized and the
field-selected indoor blower off delay begins. The
combustion air inducer begins a 20 second post-purge
period.
8.
When the combustion air post purge period is complete,
the inducer is de-energized. The indoor blower is de-
energized at the end of the off delay.
Applications Using A Single-Stage Thermostat
C - Heating Sequence — Control Thermostat Selection
DIP switch in "Single Stage" Position
1.
On a call for heat, thermostat first stage contacts
close sending a signal to the integrated control. The
integrated control runs a self-diagnostic program and
checks high temperature limit switches for normally
closed contacts and pressure switches for normally
open contacts. The combustion air inducer is energized
at the ignition speed, which is approximately the same
as the inducer speed at 70 percent firing rate.
2.
Once the control receives a signal that the low fire
pressure switch has closed, the combustion air inducer
begins a 15 second pre-purge at the ignition speed.
3.
After the pre-purge is complete, a 20 second initial
ignitor warm up period begins. The combustion air
inducer continues to operate at the ignition speed.
4.
After the 20 second warm up period has ended, the
gas valve is energized and ignition occurs, which
initiates a 10 second ignition stabilization delay. At the
same time, the control module sends a signal to begin
an indoor blower 30 second ON delay. When the delay
ends, the indoor blower motor is energized at a speed
which is appropriate for the firing rate. After the 10
second ignition stabilization delay expires, the inducer
speed is adjusted to 40 percent speed. The integrated
control also initiates a second-stage on delay (factory
set at 7 minutes; adjustable to 12 minutes).
5.
If the heating demand continues beyond the second
stage on delay, the integrated control energizes the
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combustion air inducer at 70 percent speed. The
indoor blower motor is adjusted to a speed which
matches the target rate. A fixed, 10 minute third stage
on delay is initiated.
6.
If the heating demand continues beyond the third stage
on delay, the integrated control energizes the inducer
at high speed. The indoor blower motor is adjusted to
a speed which is appropriate for the target rate.
7.
When the thermostat heating demand is satisfied,
the gas valve is de-energized and the combustion
air inducer begins a 20 second post purge. The field
selected indoor blower off delay begins.
8.
When the combustion air post purge period is complete,
the inducer is de-energized. The indoor blower is de-
energized at the end of the off delay.
Service
ELECTRICAL SHOCK, FIRE, OR EXPLOSION
Failure to follow safety warnings exactly could result in
dangerous operation, 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. Take care to reconnect wires correctly.
Verify proper operation after servicing.
At the beginning of each heating season, system should
be checked as follows by a qualified service technician:
Blower
Check the blower wheel for debris and clean if necessary.
The blower motors are pre-lubricated for extended bearing
life. No further lubrication is needed.
Blower access panel must be securely in place when
blower and burners are operating. If panels are left off,
gas fumes, which could contain carbon monoxide, can
be drawn into living space resulting in personal injury
or death.
Issue 2241
WARNING
HAZARD
WARNING
507029-05
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