Lennox G61MPV Service Manual page 41

B−Blower Compartment Figure 7
Power Choke
Blower Motor
(5 Ton Only)
To Remove Blower From Unit: Remove Bolts and
Wiring Jackplugs. Then Slide Out Front of Unit.
FIGURE 7
Secondary Limit (S21)
The secondary limits (S21) on G61MPV units are located in
the blower compartment on the back side of the blower hous-
ing. See figure 7. All G61MPV units are equipped with two sec-
ondary limits. When excess heat is sensed in the blower
compartment, the limit will open. If the limit is open, the furnace
control energizes the supply air blower and closes the gas
valve. The limit automatically resets when unit temperature re-
turns to normal. The switch is factory set to open at 125°F
and cannot be adjusted.
Blower Motor (B3)
Blower motors are manufactured by GenTeq (formally G.E.)
and Emerson. See figures 8 and 9. Motors operate the same
and are only different in physical appearance. They are both
three-phase, electronically controlled DC brushless motors
(controller converts single−phase AC to three−phase DC),
with a permanent magnet type rotor (figure 8). Because these
motors have a permanent magnet rotor it does not need
brushes like conventional DC motors.
Internal components for both manufactured motors are simi-
lar and shown in figure 10. The stator windings are split into
three poles which are electrically connected to the controller.
This arrangement allows motor windings to turn on and off
in sequence by the controller.
A solid-state controller is attached to the motor. The
controller is primarily an AC to DC converter. Converted
DC power is used to drive the motor. The controller con-
tains a microprocessor which monitors varying condi-
tions inside the motor (such as motor workload). The
controller on the Emerson motor includes the 16X4W
control with three LED's PW, RX and TX located on the
face for troubleshooting. Figure 9 shows the location of
the 16X4W and table 27 the LED codes.
SECONDARY
LIMITS (2)
(B3)
GenTeq BLOWER MOTOR B3
MOTOR
EMERSON BLOWER MOTOR B3
MOTOR
G61MPV BLOWER MOTOR COMPONENTS
The controller uses sensing devices to sense what position
the rotor is in at any given time. By sensing the position of the
rotor and then switching the motor windings on and off in se-
quence, the rotor shaft turns the blower.
All G61MPV blower motors use single phase power. An
external run capacitor is not used. The motor uses per-
manently lubricated ball-type bearings.
Each time the controller switches a stator winding (figure 10)
on and off, it is called a pulse." The length of time each pulse
stays on is called the pulse width." By varying the pulse width
(figure 13), the controller varies motor speed (called pulse-
width modulation"). This allows for precise control of motor
speed and allows the motor to compensate for varying load
conditions as sensed by the controller. In this case, the control-
ler monitors the static workload on the motor and varies motor
rpm in order to maintain constant airflow (cfm).
The motor controller is driven by the Two−stage Variable
Speed Integrated control board. The board receives its
demand (PWM signal or fixed 24 VAC or VDC signal) from
optional controls such as the Harmony IIIt zoning system,
SignatureStatt, Efficiency Plus Humidity Control (CCB1) or a
conventional thermostat.
Page 41
CONTROLLER
FIGURE 8
CONTROLLER
FIGURE 9
STATOR
(WINDINGS)
BEARING
OUTPUT
SHAFT
ROTOR
FIGURE 10
Internal Operation
J48
J49
J49
16X4W
J48