Sterling MS - Manual (Page 17)

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The gas valve consists of two operators which provide
gas to the pilot and main burners. Both operators are
energized and de-energized by the ignition control
module each heating cycle.
The pilot burner includes an ignitor and fl ame sense
probe. The ignitor provides the spark, originating at the
ignition control module, to light the pilot. The ignition
control module proves and monitors the pilot fl ame
through the fl ame sensing probe.
SEQUENCE OF OPERATION
All units follow the same basic sequence of operation
and is as follows:
1. Thermostat calls for heat. Draftor relay energizes
draftor with call for heat.
2. Pressure switch closes circuit to ignition control
module.
3. Ignition control module energizes pilot operator of gas
valve and initiates spark at ignitor of the pilot burner.
4. Pilot burner ignition is proven to the ignition control
by the fl ame sense probe and sparking of the ignitor
is discontinued.
5. Once pilot burner operation is proven, the ignition
control module energizes the main burner operator of
the gas valve, allowing gas fl ow to the main burners.
6. Approximately 60 seconds after the main burners
light, the fan time delay initiates fan operation.
7. Thermostat is satisfied and call for heat is
removed. Draftor relay de-energizes draftor with
removal of call for heat.
8. Ignition control module de-energizes pilot and main
burner operators of the gas valve, ceasing all gas fl ow.
9. Approximately two minutes after satisfying the
thermostat, fan operation ceases.
OPTIONAL GAS CONTROLS
These units are available with optional gas controls
which will give either multi-stage or modulating operation.
The sequence of operation of those units equipped with
these optional gas controls differs only at what rate each
duct furnace’s main burners ignite and operate at, or the
order of duct furnace fi ring for those units equipped with
two or three duct furnaces.
Two Stage Units: Two stages of heating; fi rst stage is
50% of full rate, second stage is 100% of full rate. Main
burner ignition is at fi rst stage only.
Three Stage Units: Dual duct furnace models: First
furnace is equipped with two stage heating; second
furnace is equipped with single stage heating but fi red
independently, giving three stages of heating.
Triple duct furnace models: Each duct furnace is
e q u i p p e d w i t h s i n g l e s t a g e h e a t i n g bu t f i r e d
independently, giving three stages. Each stage is 33%
of the unit’s full input rate. Duct furnace one will always
light fi rst and disengage last.
Four Stage Units: Dual duct furnace models only. Each
duct furnace is equipped with two stage heating but fi red
independently, giving four stages. Each stage is 25% of
the units full input rate. Duct furnace one will always light
fi rst and disengage last.
Six Stage Units: Triple duct furnace models only. Each
duct furnace is equipped with two stage heating but fi red
independently giving six stages. Each stage is 16.5% of
the units full input rate. Duct furnace one will always light
fi rst and disengage last.
Electronic Modulation Units: These units are equipped
with an electronic modulating control which provides unit
fi ring capabilities of 50 to 100% of the units full input
rate. This control is found in the gas train downstream
of the gas valve and allows main burner ignition only at
the maximum rate. A thermostat with remote setpoint
adjustment modulates the gas input.
Multi-Stage w/Electronic Modulation Units:These
dual and triple duct furnace models are equipped with
an electronic modulating control on duct furnace one
and single or two stage heating on each successive
duct furnace. Furnace one (modulated) will fi re fi rst and
disengage last. Additional stages of heat will engage
after furnace one has fi red at maximum modulation
capability for the duration of the delay setting. The
amount of modulation and each stage size depends upon
unit size and the number of stages. See following chart.
Modulation Stage
Number Capabilities Size
of Stages (% of full input) (% of full input)
2 25 - 50 50
3 16.5 - 33 33
4 25 -50 25
6 16.5 - 33 16.5