10
P/N 30149, Rev. G [12/15/2016]
WARNING
Electrical shock hazard. Turn OFF electrical power
supply at service panel before opening blower
access door. Failure to do so could result in death or
serious injury.
!
21b. Circulating Air Blower (BMLV)
BMLV furnace models are equipped with electronically
commutated motors (ECM).
Setting Blower Speed and “ON” and “OFF” Timings
Blower speed and on/off time delays are handled by ECM
motor programming and are set via dipswitches per Table
A-9 on page 17. Heating airflow rate is SW1 and on/off
delay is SW4, both are set according to firing rate. Cooling
airflow rate is SW2 and if used is set according to installed
cooling capacity. SW3 can be used to adjust airflow rate by
(+) or (-) 15%. Features of this ECM variable speed motor
are that it will deliver a constant airflow within a wide range
of external static pressures, and also includes:
• Soft Start:
ECM will slowly ramp up to required
operating speed. In heating cycle allows heat
exchanger to reach operating temperature before set
heat speed, minimizes noise and increases comfort.
• Soft Stop:
At end of heating cycle, ECM will slowly
ramp down. Allows increased energy efficiency and
reduced noise levels.
•
Dehumidification:
Dehumidification feature is
programmed into the variable speed motor. At start
of each cooling cycle, variable speed motor will run
at 82% of rated airflow for 7.5 minutes. After 7.5
minutes has elapsed, motor will increase to 100% of
rated airflow. Used to provide dehumidification and
improve system efficiency.
• Continuous Fan Operation:
When thermostat
continuous fan (G) switch is on without call for
heating or cooling, indoor fan is immediately
energized up to 50% of cooling speed. Allows
continuous circulation of air between calls for heating
or cooling. If call for heat (W) or cool (Y) occurs
during continuous fan, blower remains energized.
•
Verify setscrew is tightened at one of the flat spots,
failure to do so will convert the variable speed pulley
to a fixed speed pulley by ruining the threads.
• Modify blower speed by changing the blower pulley.
Smaller blower pulley will cause the blower to turn
faster. Large pulley reduces blower speed.
• Large increases in the blower speed may increase
power requirements.
• Check amperage draw of the blower motor after
making changes. If amperage draw is greater than
the value listed on the motor rating plate, replace
with motor of higher horsepower.
•
Deflection of 3/4 of an inch to 1 inch fan belt tension
is necessary. Less deflection places a strain on the
blower bearings and increases start up amperage
draw.
•
More deflection allows excess slippage and causes
premature motor pulley wear.
• Automotive belt dressings are not recommended.
• Bar soap will work as belt dressing to reduce belt
squeaks, etc. If using soap apply to the sides of belt
only.
If operating belt drive blower at speeds above 1100
RPM, replace sintered bronze blower bearings with roller
bearings.
