Sterling RT - Manual (Page 14)

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OPERATION continued
CONTROLS
Electronic modulating gas firing is available from the
factory on natural and propane gas units.
Do not use a thermostatic fan control switch when
either two-stage firing or modulated gas controls are
used. A fan time delay switch can be used, however,
and is available as an option on outdoor duct furnaces.
All controls are located on the access side of the unit.
Chart 5 lists orifi ce sizes for outdoor duct furnaces.
OPERATING HIGH LIMIT CONTROL
The operating limit control is a factor y installed
component surface mounted in the inlet air stream end
of the heat exchanger. This surface mounted safety
device must have adequate contact to the rear header
plate of the heat exchanger to insure its function.
When the temperature reaches the limit set point, all
heat is shutoff. The limit control has a built in auto-
reset that comes on when the equipment is suffi ciently
cooled down. Reference the unit's wiring diagram.
PILOT CONTROL
Intermittent pilot ignition is standard on all outdoor unit
sizes. Intermittent pilot ignition contains a solid state
ignition control system that ignites the pilot by spark for
each cycle of operation. When the pilot fl ame is proven,
the main burner valve opens to allow gas flow to the
burners. Both the pilot and burners are extinguished
during the off cycle.
HIGH GAS LINE PRESSURE REGULATOR
(Natural Gas only)
The pressure regulator is a field installed component
located external of the unit and as close as possible to
where the gas line inlet enters the unit.
The pressure regulator reduces the main gas line
pressure to a minimum of seven inches WC (1.74 kPa).
Chart 4 - Gas Supply Pressure
Heating Value
Natural Gas Propane Gas
1075 Btu/Ft 3 2500 Btu/Ft 3
(40.1 MJ/m 3 ) (93.1 MJ/m 3 )
Manifold Pressure
Single Stage Application 3.5 inch WC 10.0 inch WC
(0.87 kPa) (2.49 kPa)
Two Stage Application - High Fire 3.5 inch WC 10.0 inch WC
(0.87 kPa) (2.49 kPa)
Two Stage Application - Low Fire 1.1 inch WC 3.8 inch WC
(0.27 kPa) (0.95 kPa)
Modulating Application - High Fire 3.5 inch WC 10.0 inch WC
(0.87 kPa) (2.49 kPa)
Modulating Application - Low Fire 0.9 inch WC 3.5 inch WC
(0.22 kPa) (0.87 kPa)
Minimum Supply Pressure
Single Stage Application 5.0 inch WC 11.0 inch WC
(1.24 kPa) (2.74 kPa)
Two Stage Application 6.5 inch WC 11.5 inch WC
(1.62 kPa) (2.86 kPa)
Modulating Application 6.5 inch WC 11.5 inch WC
(1.62 kPa) (2.86 kPa)
Maximum Supply Pressure 14.0 inch WC 14.0 inch WC
(3.49 kPa) (3.49 kPa)