Lennox Allied Air A96UHMV, Installation Instructions Manual

Page: 53 / 66

506550-01 Page 53 of 66 Issue 1230
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
fieldselected 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 prepurge at the ignition speed.
3. After the prepurge 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 35 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
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, 1O minute third stage
on delay is initiated.
6. If the heating demand continues beyond the thirdstage
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.