Variable Speed Vent Motor - American Standard 50A65-475 Manual

Variable Speed Vent Motor

This microprocessor based variable speed motor
ECM TM has an adaptive learning routine, which causes
the motor to learn the optimum operating speed for
low and high fire. The adaptive learning routine causes
the motor to learn the lowest possible operating speed
to ensure proper gas combustion at its maximum
efficiency level.
The motor microprocessor works in conjunction
with two pressure switches, one set for the correct
low fire combustion air pressure and the other for
high fire combustion air pressure. These switches are
normally open.
How Does It Learn?
The adaptive learning routine begins on the initial
call for heat, after power has cycled. On the initial call
for heat, "W1" first stage, the motor ramps up to
speed and checks the low pressure switch (LPS) input
to verify that the switch is closed. After running for one
minute, the motor ramps to its over-blow speed, which
is 200 to 300 rpms higher, and runs at that speed for
one minute, then begins to drop its speed until the
LPS opens. When the LPS opens, the motor speed is
increased slightly in steps until the LPS closes.
The motor will run at this speed for the next 150
calls for first stage heat, "W1" . On a call for second
stage heat, "W2, " the motor ramps up to high speed
and the high speed pressure switch (HPS) input is
checked to verify the switch has closed.
After running for 90 seconds, the motor begins to drop
its speed until the HPS opens. When the HPS opens, the
motor speed is again increased slightly in steps until
the HPS closes.The motor will run at this speed for the
next 50 calls for second stage heat, "W2" .
The learning process is repeated after the cycle count is
completed for each stage. Both are learned after power
is cycled.
The pressure switches are constantly monitored during
the furnace operation. If a pressure switch opens during
a run cycle, the motor speeds up to close the switch
and maintains proper combustion air.
If during the second stage cycle the HPS opens for
any reason, the motor will speed up gradually, every
3 to 4 seconds, attempting to close the HPS. The motor
will continue to do this until it reaches its speed limit.
If this occurs, the motor returns to Low Fire rpm for
10 minutes, at which time, the motor will attempt
to close the HPS again. The IFC will continue this
sequence as long as there is a call for "W2" heat and
HPS does not close.
If LPS opens during a call for heat, the motor will
speed up gradually, every 3 to 4 seconds, until Low Fire
speed limit is reached. If the LPS is not closed during
this process, the furnace will shut down and indicate a
3 flash fault. A recycle will occur in about 30 seconds.
Motor speeds are primarily dependent on vent
applications and combustion cycle restrictions.
Part # BLW00662 Variable Speed Vent Motor
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