SERVICING
37
B. Shorted - indicator swings to zero and stops there -
replace.
C. Open - no reading - replace. (Start capacitor would
read resistor resistance.)
S-15B CAPACITANCE CHECK
Using a hookup as shown below, take the amperage and
voltage readings and use them in the formula:
VOLTMETER
CAPACITOR
AMMETER
15 AMP
FUSE
TESTING CAPACITANCE
WARNING
Discharge capacitor through a 20 to 30 OHM
resistor before handling.
Capacitance (MFD) = 2650 X Amperage
Voltage
S-16A CHECKING FAN AND BLOWER MOTOR
WINDINGS (PSC MOTORS)
The auto reset fan motor overload is designed to protect the
motor against high temperature and high amperage condi-
tions by breaking the common circuit within the motor, similar
to the compressor internal overload. However, heat gener-
ated within the motor is faster to dissipate than the compres-
sor, allow at least 45 minutes for the overload to reset, then
retest.
1. Remove the motor leads from its respective connection
points and capacitor (if applicable).
2. Check the continuity between each of the motor leads.
3. Touch one probe of the ohmmeter to the motor frame
(ground) and the other probe in turn to each lead.
If the windings do not test continuous or a reading is obtained
from lead to ground, replace the motor.
S-16B CHECKING FAN AND BLOWER MOTOR
(ECM MOTORS)
An ECM is an
Electronically Commutated Motor
which offers
many significant advantages over PSC motors. The ECM
has near zero rotor loss, synchronous machine operation,
variable speed, low noise, and programmable air flow. Be-
cause of the sophisticated electronics within the ECM
motor, some technicians are intimated by the ECM motor;
however, these fears are unfounded. GE offers two ECM
motor testers, and with a VOM meter, one can easily perform
basic troubleshooting on ECM motors. An ECM motor
requires power (line voltage) and a signal (24 volts) to
operate. The ECM motor stator contains permanent magnet.
As a result, the shaft feels "rough" when turned by hand. This
is a characteristic of the motor, not an indication of defective
bearings.
WARNING
Line Voltage now present.
1. Disconnect the 5-pin connector from the motor.
2. Using a volt meter, check for line voltage at terminals #4
& #5 at the power connector. If no voltage is present:
3. Check the unit for incoming power See section S-1.
4. Check the control board, See section S-40.
5. If line voltage is present, reinsert the 5-pin connector and
remove the 16-pin connector.
6. Check for signal (24 volts) at the transformer.
7. Check for signal (24 volts) from the thermostat to the "G"
terminal at the 16-pin connector.
8. Using an ohmmeter, check for continuity from the #1 &
#3 (common pins) to the transformer neutral or "C"
thermostat terminal. If you do not have continuity, the
motor may function erratically. Trace the common cir-
cuits, locate and repair the open neutral.
9. Set the thermostat to "Fan-On". Using a voltmeter,
check for 24 volts between pin # 15 (G) and common.
10. Disconnect power to compressor. Set thermostat to call
for cooling. Using a voltmeter, check for 24 volts at pin #
6 and/or #14.
11. Set the thermostat to a call for heating. Using a voltme-
ter, check for 24 volts at pin #2 and/or #11.
