Sequence of Operation (Modulating Burner)
Low Heat Option with Modulation
The following details the sequence of operation for the low
heat option.
1 .
Unit DDC controller calls for heat.
2 .
Furnace DDC control module receives a call for heat.
3 .
Furnace safety switches and DDC control are checked
for safe conditions.
4 .
45 second prepurge cycle starts. Proof of airflow switch
is checked for combustion airflows.
5 .
Spark ignitor is activated.
6 .
Gas valve receives a signal to open fully.
7 .
Burner is ignited and runs for 20 seconds in high fire.
NOTE:
If call for heat is interrupted during this timing, the
furnace will be locked in for the 20 seconds cycle.
8 .
Gas valve and induction blower motor receives a signal
to modulate burner output to match the unit discharge air
temperature setting.
High Heat Option with Modulation
The following details the sequence of operation for the high
heat option. This option includes dual burners with one being
modulating and the other being 2 stage control.
1 .
Unit DDC controller calls for heat.
2 .
Top Furnace DDC control module receives a call for heat.
3 .
High limit switch is checked for safe condition.
4 .
Proof of airflow switch is checked for combustion airflow.
5 .
45 second prepurge cycle starts.
6 .
Spark ignitor is activated.
7 .
Gas valve receives a signal to open fully.
8 .
Burner is ignited and runs for 30 seconds in high fire
9 .
Modulating burner gas valve and induction blower motor
receives a signal to modulate burner output to match the
unit discharge air temperature setting.
10 .
If modulating burner is unable to meet discharge
temperature set point, furnace DDC control calls for
third stage of heating. The top furnace is reduced to
low (50%) fire. The bottom furnace is sequenced on per
stage furnaces sequence of operation (steps 2 - 8).
11 .
Staged burner gas valve receives a signal to open to 50%.
12 .
Modulating burner gas valve and induction blower motor
receives a signal to modulate burner output to match the
unit discharge air temperature setting.
13 .
If stage 3 and modulating furnace is unable to meet
discharge temperature setpoint, furnace DDC controller
calls for stage 4 heat. The bottom furnace will stage up to
high fire and the modulating furnace will reduce to 50%
operation .
14 .
Staged burner gas valve receives a signal to open fully.
15 .
Modulating furnace's gas valve and induction blower
motor receives a signal to modulate burner output to
match the unit discharge air temperature setting.
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IM 1058-8 • MAVERICK II ROOFTOP SYSTEMS
