Lennox EL296UH110XV60C - Page 94

Page 94
Applications Using A Single-Stage Thermostat See
FIGURE 60 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 satised after the eld adjustable period (7 or 12
minutes).
1 - On a call for heat, thermostat rst-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 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 re pressure switch does not close
the combustion air inducer will switch to high re.
After a 15 second pre-purge the high re pressure
switch will close and the unit will begin operation on
high re. After 10 to 20 seconds of high re operation
the unit will switch to low re.
3 - After the pre-purge is complete, a 20-second initial
ignitor warm-up period begins. The combustion air
inducer continues to operate at low speed.
4 - After the 20-second warm-up period has ended, the
gas valve is energized on low re (rst stage) and
ignition 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
motor is energized on the low re 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 re (second stage) pressure
switch to make sure it is closed. The high re
(second stage) gas valve is energized and the indoor
blower motor is energized for operation at the high
re heating speed.
6 - When the thermostat heating demand is satised,
the combustion air inducer begins a 5-second low
speed post-purge. The eld-selected indoor blower
o󰀨 delay begins. The indoor blower operates at the
low-re heating speed.
7 - When the combustion air post-purge period is
complete, the inducer, the HUM contacts as well
as the 120V ACC terminals are de-energized. The
indoor blower is de-energized at the end of the o󰀨
delay.
1 stg heat demand
2 stg heat demand
15
ON
OFF
low speed CAI
35
1
Pre-Purge
Ignitor Warm-up
30 second
blower
“on” delay
Post
Purge
5 SEC80
ignitor
HEATING OPERATION WITH TWO-STAGE THERMOSTAT
low fire gas valve
indoor blower low heat
high speed CAI
high fire gas valve
indoor blower high heat
39
Trial For
Ignition
blower
“off”
delay
RECOGNITION PERIOD
30 seconds
FIGURE 59
heat demand
15
ON
OFF
low speed CAI
35
1
Pre-Purge
Ignitor Warm-up
30 second
blower
“on” delay
Post
Purge
5 SEC80
ignitor
HEATING OPERATION WITH SINGLE STAGE THERMOSTAT
low fire gas valve
indoor blower low heat
high speed CAI
high fire gas valve
indoor blower high heat
39
Trial For
Ignition
blower
“off”
delay
7 or 12 minutes after heating demand begins, furnace switches to high fire (depending on setting)
FIGURE 60