Lennox EL296UHVX Series Unit Information page 42

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 EL296UHV 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 con­
stant static pressure against the blower wheel. The controller
monitors 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 rel­
atively stable over a broad range of static pressure. Since the
blower constantly adjusts rpm to maintain a specified cfm, mo­
tor rpm is not rated. Hence, the terms "cool speed", "heat
speed " or "speed tap" in this manual, on the unit wiring dia­
gram and on blower B3, refer to blower cfm regardless of mo­
tor 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.
Motor Start‐Up
When B3 begins start‐up, the motor gently vibrates back and
forth for a moment. This is normal. During this time the elec­
tronic controller is determining the exact position of the rotor.
Once the motor begins turning, the controller slowly eases
the motor up to speed (this is called "soft‐start"). The motor
may take as long as 10‐15 seconds to reach full speed. If the
motor does not reach 200 rpm within 13 seconds, the motor
shuts down. Then the motor will immediately attempt a
restart. The shutdown feature provides protection in case of a
frozen bearing or blocked blower wheel. The motor may at­
tempt to start eight times. If the motor does not start after the
eighth try, the controller locks out. Reset controller by momen­
tarily turning off power to unit.
The DC filter capacitors inside the controller are connected
electrically to the motor supply wires. The capacitors take
approximately 5 minutes to discharge when the disconnect
is opened. For this reason it is necessary to wait at least 5
minutes after turning off power to the unit before attempt­
ing to service motor.
Disconnect power from unit and
wait at least five minutes to allow
capacitors to discharge before at­
tempting to service motor. Failure
to wait may cause personal injury
or death.
Power Choke (L13)
A choke coil is used on EL296UHV 4 and 5 ton units
equipped with 1 hp motors. The choke is located on the
blower housing and is used to suppress transient current
spikes.
Troubleshooting Motor Operation
To verify motor operation see steps below and figures 9
and 10.
1- Remove J48 (5 pin power plug) from P48 on the mo­
tor.
2- With the power on at the furnace and door switch de­
pressed, use a test meter to verify 120V between pins
4 and 5 on J48.
3- Reconnect J48 to P48 on the motor.
4- Remove J49 (4 pin low voltage connector) from P49
on the motor.
5- Using test jumpers, apply 24V to pins 3 and 4 on P49
on the motor.
Note: Do not apply 24V to pins 2 and 4 on P49. Doing so
will cause permanent damage to the motor.
6- Motor should run at 75%.
7- Test is complete. Remove jumpers and reconnect
plugs.
Another option is to use the TECMate PRO motor tester
with the 16 to 4 pin adaptor. The use of the TECMate PRO
isolates the motor from the integrated control. Follow the
instructions provided with the kit. If the motor runs do not
replace.
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