Armstrong Air Conditioning A97DSMV, Installation Instructions Manual

Page: 54 / 68

507029-03 Page 54 of 68 Issue 1622
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 fi r i ng 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 i ncreased by 10 percent every
5 minutes until the call for heat i s satisfied or the furnace
reaches 100 percent rate . As the firing rate increases ,
the i ndoor blowe r motor is adjusted to a speed which
is appropriate for the target rate .
6. If second-stage heat demand is satisfi ed , but first stage
is still present , the furnace will continue to operate at
the present firing rate until the heat cyc l e ends .
7. When the demand for first and second stage heat
is satisfied , the gas valve is de-energized and the
fieldselected indoor blower off delay begins . The
combustion air inducer begins a 20 second post-purge
per i od .
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 i nducer is energized
at the ignition speed , which i s 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 prepurge at the i gnition speed .
3. After the prepurge is complete , a 20 second i nitial ignitor
warm up period begins. The combustion air inducer
continues to operate at the ign i tion 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 appropr i ate 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
m i nutes ; adjustable to 12 minutes) .
5. If the heat i ng demand continues beyond the secondstage
on delay , the integrated control energizes the 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 thirdstage
on delay , the integrated control energ i zes the inducer
at high speed . The indoor blower motor i s 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 i ndoor 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 .