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B−Blower Compartment (Figure 7)
FIGURE 7
Power Choke
(4 and 5 Ton Only)
Blower Motor
(B3)
To Remove Blower From Unit: Remove access panels,
Control box, Bolts and Wiring Jackplugs.
Then Slide Out Front of Unit.
1. Blower Motor (B3)
WARNING
During blower operation, the ECM motor emits ener-
gy that may interfere with pacemaker operation. Inter-
ference is reduced by both the sheet metal cabinet
and distance.
The SLP98UHV line uses three different motor sizes; 1/2 hp,
3/4 hp and 1hp. The motor communicates with the integrated
control via a 2−way serial connection. The motor receives all
necessary functional parameters from the integrated control
and does not rely on a factory program like traditional variable
speed motors. SLP98UHV units use a three-phase, electroni-
cally controlled D.C. brushless motor (controller converts
single phase a.c. to three phase D.C.), with a permanent-
magnet-type rotor (figure 8). Because this motor has a perma-
nent magnet rotor it does not need brushes like conventional
D.C. motors.
Internal components are shown in figure 8. The stator wind-
ings 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.
IMPORTANT
Earlier ECM motors used on other Lennox furnace
models are not interchangeable with motors used on
the SLP98UHV furnace line.
A solid-state controller is permanently attached to the
motor. The controller is primarily an A.C. to D.C. convert-
er. Converted D.C. power is used to drive the motor. The
controller contains a microprocessor which monitors
varying conditions inside the motor (such as motor work-
load).
SLP98UHV BLOWER MOTOR COMPONENTS
FIGURE 8
STATOR
(WINDINGS)
BEARING
ROTOR
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 SLP98UHV blower motors use single phase power.
An external run capacitor is not used. The motor uses
permanently lubricated ball-type bearings.
Internal Operation
The motor is controlled via serial communication between
the integrated control on the furnace and the controller at-
tached to the motor shell. The messages sent back and
forth between the two controls serve to communicate rota-
tional direction, demand, motor size, current draw, torque,
and rpm, among other variables.
Motor rpm is continually adjusted internally to maintain constant
static pressure against the blower wheel. The controller moni-
tors the static work load on the motor and motor amp-draw to
determine the amount of rpm adjustment. Blower rpm may be
adjusted any amount in order to maintain a constant cfm as
shown in Blower Ratings Tables. The cfm remains relatively
stable over a broad range of static pressure. Since the blower
constantly adjusts rpm to maintain a specified cfm, motor rpm is
not rated. Hence, the terms cool speed", heat speed " or
speed tap" in this manual, on the unit wiring diagram and on
blower B3, refer to blower cfm regardless of motor rpm.
Initial Power Up
When line voltage is applied to B3, there will be a large inrush
of power lasting less than 1/4 second. This inrush charges a
bank of DC filter capacitors inside the controller. If the discon-
nect switch is bounced when the disconnect is closed, the dis-
connect contacts may become welded. Try not to bounce the
disconnect switch when applying power to the unit.
