9
P/N 30149, Rev. G [12/15/2016]
19. Burner Primary (Safety) Control
Furnace is equipped with primary combustion control, also
referred to as burner relay or burner protector relay, which
uses a cad cell located in burner housing, to monitor and
control combustion.
Dust or combustion residuals can build up on lens of cad
cell impairing its response to flame. Check cad cell for
cleanliness and proper alignment if primary control fre
-
quently shuts down combustion.
20. Combustion Chamber
Furnace is equipped with cerafelt combustion chamber, held
in place by a retaining bracket.
Check the alignment of the combustion chamber
and oil burner before firing. It is possible for the
combustion chamber to shift if subjected to rough
handling during transit.
Inspect combustion chamber for damage or carbon build
up whenever oil burner is removed for repairs or routine
maintenance.
WARNING
Fire, burn, asphyxiation hazard. Do not start the
burner unless blower access door is secured in
place. Failure to follow these instructions could
result in death or serious injury.
!
21a. CIRCULATING AIR BLOWER (BML/BMLV)
• BML furnace models may be equipped with either
direct drive or belt drive blower systems.
• BMLV furnace models are equipped with direct drive
blower systems.
• BML models are equipped with PSC motors.
• BMLV models are equipped with electronically
commutated motors (ECM).
Direct Drive Blower Systems
• Direct drive blower speed adjustments are not
normally required in properly sized extended plenum
duct systems. Motor RPM and air CFM delivery will
vary automatically to accommodate conditions within
usual range of external static pressures typical of
residential duct systems.
•
Under-sized duct systems may require higher blower
speed to obtain system temperature rise.
• Some older duct systems were not designed to
provide static pressure. They typically feature special
reducing fittings at each branch run and lack block
ends on the trunk ducts. These systems may require
modification to provide some resistance to the airflow
to prevent over-amping of direct drive blower motor.
Selecting a lower blower speed may correct this
problem.
• Direct drive blower speeds are adjusted by changing
"hot" wires to motor winding connections. Refer to
wiring diagrams in Appendix B or wiring diagram
label affixed to furnace.
• Do not move neutral wire (normally white
wire) to adjust blower speed.
• Single blower speed for both heating and cooling
modes may be used. Use a "piggy-back connector"
accommodating both wires on a single motor tap.
• It is also acceptable to connect selected motor speed
with a pigtail joined to both heating and cooling
speed wires with a wire nut.
• Safety precaution against accidental disconnection of
wires by vibration, secure wire nut and wires with few
wraps of electricians tape.
• Do not connect power leads between motor
speeds. Always connect neutral wire to motor's
designated neutral terminal.
• If joining blower speed wiring is done in furnace
junction box, tape off both ends of unused wire.
• Do not use blower speed wires as source of
power to accessories as electronic air cleaners
and humidifier transformers. Unused motor
taps auto-generate sufficiently high voltages to
damage accessory equipment.
Belt Drive Blower Systems
WARNING
Improper installation could result in death or serious
injury. Belt drive components operate at high speeds
and may snag loose clothing resulting in injury or
death. Have a trained service professional preform
the following instructions. Failure to follow these
instructions could result in death or serious injury.
!
Belt drive blower systems can be modified for speed and
air delivery by adjusting variable speed motor pulley and
changing blower pulley.
• Adjust variable speed motor pulley by loosening 5/32
allen set screw in outer sheave. Turn outer sheave
clockwise to increase blower speed, counter clockwise
to reduce speed.
NOTICE
Do not tamper with furnace controls they are
sensitive. If problems persist, call your service
contractor.
