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Application Using a Single Stage Thermostat
B - Heating Sequence - Integrated Control Thermostat
Selection DIP switch 1 ON in "Single-Stage" Position
NOTE: In these applications, two-stage heat will be initiated
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
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 prepurge 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 prepurge is complete, a 20 second initial ignitor
warm-up period begins. The combustion air inducer
continues to opeate at the ignition speed.
507404-04
4.
After the 20-second warm-up period has ended, the
gas valve is energized on low fire (first 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 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 delay
begins. The indoor blower operates at the low-fire
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 off delay.
Figure 29
Figure 30
Issue 1621
Page 67 of 80
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