SERVICING
65
Electrical Checks - High Voltage Power Circuits
HIGH VOLTAGE!
Disconnect ALL power before servicing
or installing. Multiple power sources
may be present. Failure to do so may
cause property damage, personal injury
or death.
1. Disconnect power to the furnace.
2. Disconnect the 5-circuit power connector to the ECM
motor.
3. Turn on power to the furnace.
WARNING
Line Voltage now present.
4. Measure voltage between pins 4 and 5 on the 5-circuit
connector. Measured voltage should be the same as the
supply voltage to the furnace.
5
4
3
2
1
Lines 1 and 2 will be connected
for 120VAC Power Connector
applications only
Gnd
AC Line Neutral Connection
AC Line Hot Connection
}
POWER CONNECTOR
(1/2 HP MOTORS)
"Motor Half“
(Viewed from Plug End)
5
4
3
2
1
Lines 1 and 2 will be connected
for 120VAC Power Connector
applications only
Gnd
AC Line Neutral Connection
AC Line Hot Connection
}
inductor
POWER CONNECTOR
(3/4 & 1 HP MOTORS)
"Motor Half“
(Viewed from Plug End)
5. Measure voltage between pins 4 and 3. Voltage should
be approximately zero.
6. Measure voltage between pins 5 and 3. Voltage should
be the same as the supply voltage to the furnace.
7. If no voltage is present, check supply voltage to the fur-
nace. See section S-1.
8. Disconnect power to the furnace. Reconnect the 5-
circuit power harness disconnected in step 2.
Electrical Checks - Low Voltage Control Circuits
1. Turn on power to the furnace.
WARNING
Line Voltage now present.
2. Check voltage between pins 1 and 4 on the 4-wire motor
control harness between the motor and control board.
Voltage should be between 9 and 15 VDC.
3. If no voltage is present, check control board. See sec-
tion S-313.
Motor Control/End Bell Checks
HIGH VOLTAGE!
Disconnect ALL power before servicing
or installing. Multiple power sources
may be present. Failure to do so may
cause property damage, personal injury
or death.
1. Disconnect power to the furnace.
NOTE:
Motor contains capacitors that can hold a charge
for several minutes after disconnecting power. Wait 5
minutes after removing power to allow capacitors to dis-
charge.
2. Disconnect the motor control harness and motor power
harness.
3. Remove the blower assembly from the furnace.
4. Remove the (3) screws securing the control/end bell to
the motor. Separate the control/end bell. Disconnect
the 3-circuit harness from the control/end bell to remove
the control/end bell from the motor.
5. Inspect the NTC thermistor inside the control/end bell
(see figure below). Replace control/end bell if thermistor
is cracked or broken.
