Lennox EL280DF070E36A Unit Information page 32

Applications Using A Single-Stage Thermostat
See FIGURE 25 for ignition control sequence
B - Heating Sequence - Integrated Control Thermostat
Selection DIP Switch 1 ON in "Single-Stage" Position
NOTE - In these applications, two-stage heat will be initi-
ated by the integrated control if heating demand has not
been satisfied after the field adjustable period (7 or 12
minutes).
1. On a call for heat, thermostat first-stage contacts close
sending a signal to the integrated control. The integrat-
ed control runs a self-diagnostic program and checks
high temperature limit switches for normally closed con-
tacts and pressure switches for normally open contacts.
The combustion air inducer is energized at low speed.
2. Once the control receives a signal that the low pressure
switch has closed, the combustion air inducer begins a
15-second pre-purge in low speed.
NOTE - If the low fire pressure switch does not close the
combustion air inducer will switch to high fire. After a 15
second pre-purge the high fire pressure switch will close
and the unit will begin operation on high fire. After 10 to
20 seconds of high fire operation the unit will switch to low
fire.
3. After the pre-purge is complete, a 20-second initial ignit-
or warm-up period begins. The combustion air inducer
continues to operate at low speed.
ON
OFF
1 stg heat demand
low speed CAI
ignitor
low fire gas valve
indoor blower low heat
2 stg heat demand
high speed CAI
high fire gas valve
indoor blower high heat
ON
OFF
heat demand
low speed CAI
ignitor
low fire gas valve
indoor blower low heat
7 or 12 minutes after heating demand begins, furnace switches to high fire (depending on setting)
high speed CAI
high fire gas valve
indoor blower high heat
HEATING OPERATION WITH TWO-STAGE THERMOSTAT
1 15
Pre-Purge
Ignitor Warm-up
30 seconds
HEATING OPERATION WITH SINGLE STAGE THERMOSTAT
1 15
Pre-Purge
Ignitor Warm-up
4 - After the 20-second warm-up period has ended, the
gas valve is energized on low fire (first stage) and ig-
nition occurs. 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 mo-
tor is energized on the low fire heating speed and the
HUM contacts are energized. 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
combustion air inducer at high speed. The control also
checks the high fire (second stage) pressure switch to
make sure it is closed. The high fire (second stage)
gas valve is energized and the indoor blower motor is
energized for operation at the high fire heating speed.
6 - When the thermostat heating demand is satisfied, the
combustion air inducer begins a 5-second low speed
post-purge. The field-selected indoor blower off de-
lay begins. The indoor blower operates at the low-fire
heating speed.
7 - When the combustion air post-purge period is com-
plete, the inducer and the HUM contacts are de-ener-
gized. The indoor blower is de-energized at the end of
the off delay as well as the 120V ACC terminal.
35 39 80
30 second
blower
Trial For
"on" delay
Ignition
RECOGNITION PERIOD
FIGURE 24
35 39 80
30 second
blower
Trial For
"on" delay
Ignition
FIGURE 25
Page 32
5 SEC
blower
"off"
Post
delay
Purge
5 SEC
blower
"off"
Post
delay
Purge