56
SSCBL-RPBL-IOM (10-22) 149159-C
CONTROLS—CONTINUED
Pilot and Ignition Systems
⚠ WARNING ⚠
Due to high voltage on the pilot spark wire and pilot electrode, do not touch when energized.
• Pilot:
The pilot (see
) is a vertical target type with lint-free feature . Pilot flame should be approximately
1-1/4” in length . Pilot gas pressure should be the same as supply line pressure (refer to
section) . Pilot gas is supplied through the combination valve; the pilot gas flow is controlled by an adjustment
screw located in the valve body .
Figure 41. Typical Burner Rack with Pilot
• Ignition system:
Natural gas units are equipped with a spark-ignited intermittent safety pilot system that shuts off
pilot gas flow between heat cycles . Propane units (or as an option on natural gas units) require a lockout device
that stops gas flow to the pilot if the pilot fails to light in 120 seconds . This lockout device has a 1-hour retry or
requires a manual reset by interruption of the thermostat circuit . Refer to the wiring diagram provided with the unit
for pilot system identification and for proper wiring . Spark pilot without lockout is designated as option AH2 or pilot
with lockout is option AH3 .
• Ignition controller:
As part of the intermittent safety pilot system, the ignition controller provides high voltage
spark to ignite pilot gas and also acts as the flame safety device . After ignition of the pilot gas, the ignition controller
electronically senses the pilot flame . A low voltage DC electrical signal is imposed on the separate metal probe
in the pilot assembly . The metal probe is electrically insulated from ground . The pilot flame acts as a conduction
path to ground to complete the DC circuit and prove pilot flame . Proper operation of the electronic spark ignition
system requires a minimum flame signal of 0 .2 microamps, as measured by a microampmeter . With pilot flame
proven, the ignition controller energizes the main gas valve .
Burners and Carryover System
• Burners:
These duct furnaces have individually-formed steel burners with accurately die-formed ports to provide
controlled flame stability without lifting or flashback with either natural or propane gas . All burners are lightweight
and are factory-mounted in an assembly that permits all of the burners to be removed as a unit for inspection or
service .
•
Natural gas burner racks (except when equipped with electronic modulation option AG39, AG40, AG41, or AG42)
are equipped with two flash carryovers . Natural gas burner racks on SSCBL units manufactured
before
1997 had
a gas lighter tube carryover and one flash carryover .
•
Propane gas burners are equipped with one flash carryover and a regulated gas lighter tube system . The carryover
lighter tube receives its gas supply through a regulator, simultaneously with the gas to the burner orifices .
Pilot
Auxiliary
Sensor
Flash Carryover
Flash
Carryover
Natural Gas Burner Rack
Carryover Lighter Tube
Pilot
Carryover
Regulator
Flash
Carryover
Propane Pilot
Auxiliary
Flame
Probe
Propane Burner Rack with Lighter Tube
Natural Gas
Pilot
