Sterling ME - Manual (Page 11)

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Drain Pan Connection
H
Total
Height
of Trap
X = 1/2 “H”
H = At Least 1 Inch Plus
Casing Static Pressure
D3887 Total Height Of Trap = X+ H + (1-1/2 X Pipe Diameter)
Unit
Housekeeping
Pad
X
IV. OPERATION
GENERAL INFORMATION
Refer to Indoor Gas-Fired Duct Furnace Installation and
Service Manual for specifi c information regarding the
heating operation of this unit.
All units are equipped with an intermittent ignition pilot
system. The pilot is lit and extinguished each cycle of unit
heating operation.
On natural gas units, the ignitor will continue to spark and
pilot gas will continue to fl ow until the pilot fl ame is proven.
LP (propane) units are equipped with 100% lockout. The
lockout function shuts off the main and pilot gas valves if
the pilot gas fails to ignite within 90 seconds of the onset
of trial for ignition.
The gas control system operates at 24 VAC and is
supplied by a stepdown transformer found in the electrical
cabinet that will match the unit line voltage specifi ed. See
Figure 8 for unit controls location.
Figure 11 - Drain Pan Connection
Do not use a thermostatic fan control switch when either
two-stage fi ring or modulated gas controls are used.
GAS CONTROL SYSTEM
The standard unit comes equipped for single stage
operation. Unit heating operation is accomplished at
full input.
Each duct furnace is equipped with an individual ignition
control system which consists of the following components:
ignition control module, gas valve and pilot burner.
The ignition control module is the heart of the ignition
control system. This control initiates all gas fl ow, provides
means to light the pilot burner, proves and monitors the
pilot burner operation.
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 (additional power vented sequences
are also described):
1. Thermostat calls for heat. (Power vented units only:
Draftor relay energizes draftor with call for heat).
2. Ignition control module energizes pilot operator of gas
valve and initiates spark at ignitor of the pilot burner.
3. Pilot burner ignition is proven to the ignition control
by the fl ame sense probe and sparking of the ignitor
is discontinued.
4. Once pilot burner operation is proven, the ignition
control module energizes the main burner operator
of the gas valve, allowing gas flow to the main
burners. (Power vented units only: In addition, draftor
operation must be proven by draftor pressure switch
before ignition control module energizes main burner
operator of gas valve).
5. Approximately 60 seconds after the main burners
light, the fan time delay initiates fan operation.
6. T h e r m o s t a t i s s a t i s f i e d a n d c a l l fo r h e a t i s
removed. (Power vented units only: Draftor relay
de-energizes draftor with removal of call for heat).
7. Ignition control module de-energizes pilot and main
burner operators of the gas valve, ceasing all gas fl ow.
8. 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.