SERVICING
32
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.
6. Inspect the large capacitors inside the control/end bell
(see figure below). Replace the control/end bell if any
of the capacitors are bulging or swollen.
7. Locate the 3-circuit connector in the control/end bell.
Using an ohmmeter, check the resistance between each
terminal in the connector. If the resistance is 100k
W
or greater, the control/end bell is functioning properly.
Replace the control/end bell if the resistance is lower
than 100k
W
.
8. Reassemble motor and control/end bell in reverse of
disassembly. Replace blower assembly into the furnace.
Motor Checks
WARNING
High Voltage!
Disconnect all power before servicing
or installing this unit. 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 discharge.
2. Disassemble motor as described in steps 2 through 4
above.
3. Locate the 3-circuit harness from the motor. Using an
ohmmeter, measure the resistance between each motor
phase winding. The resistance levels should be equal.
Replace the motor if the resistance levels are unequal,
open circuited or short circuited.
4. Measure the resistance between each motor phase
winding and the motor shell. Replace the motor if any
phase winding is short circuited to the motor shell.
5. Reassemble motor and control/end bell in reverse of
disassembly. Replace blower assembly into the furnace.
To determine proper air movement, proceed as follows:
1.
With clean filters in the furnace, use a draft gauge
(inclined manometer) to measure the static pressure
of the return duct at the inlet of the furnace. (Negative
Pressure)
2. Measure the static pressure of the supply duct. (Positive
Pressure)
3. Add the two (2) readings together for total external static
pressure.
NOTE: Both readings may be taken simultaneously
and read directly on the manometer if so
desired. If an air conditioner coil or Electronic
Air Cleaner is used in conjunction with the
furnace, the readings must also include theses
components, as shown in the following drawing.
4. Consult proper tables for the quantity of air.
If the total external static pressure exceeds the minimum
or maximum allowable statics, check for closed dampers,
registers, undersized and/or oversized poorly laid out duct
work.
