compressor, the PTC device's low resistance shorts out the run capacitor; thus producing
adequate motor starting torque.
As the compressor motor approaches run-ning speed, the current through the PTC device
causes the temperature and resistance of the PTC device to increase to where it appears to be
an open circuit. The compressor continues to operate on the run winding in parallel with the
series combination of the run capacitor and start winding.
Checking the PTC Device
1. Disconnect the unit from the power source.
2. Discharge the capacitor and remove the wires from the PTC device terminals.
3. Allow the PTC to cool to room temperature.
4. Remove the PTC device.
5. Using an ohmmeter, check the resistance between the PTC device terminals. The ohmmeter
should register between 3 and 20 ohms. An extreme variance between 3 and 20ohms
indicates a defective PTC device which must be replaced.
8.4.9 RUN CAPACITOR
The run capacitor is mounted adjacent to the compressor. It is electrically connected to the
compressor circuit to provide the required phase difference between the start and run windings
for running the compressor.
Capacitor Failures May Be Caused By:
(1) A Short Circuit - Will cause the start windings to be energized continuously in the start mode.
The compressor could start, but the overload protector will trip, and eventually trip continuously.
(2) An Open Circuit - Should, under normal conditions, allow the compressor to start. Under a
heavy running load, however, the compressor will trip on the overload.
(3) A Capacitor Low in Capacitance – A capacitor may lose capacitance by a loss of its
electrolytic properties. The compressor would run under a light load, but would trip on the
overload in high ambient conditions.
Testing the Capacitor
We recommend using a capacitor analyzer when testing. A solid state unit that measures
capacitance and power of any capacitor, and has an automatic means of discharging the
capacitor through resistance is preferred.
Alternate Method Ohmmeter
1. Disconnect the unit from the power source.
2. Disconnect the capacitor lead wires.
3. Short across the terminals using a resistor with a minimum resistance of 1,000 ohms. This
ensures that no charge remains to damage the ohmmeter.
4. Set the ohmmeter selector switch to the 10,000 ohm scale (R x 10K).
5. Connect the ohmmeter leads to the capacitor terminals and observe the meter point lower
end.
If the pointer deflects to the lower end and remains there, the capacitor is shorted and
must be replaced.
If there is no deflection of the pointer, the capacitor is open and must be replaced.
If the pointer deflects toward the high end of the scale and then slowly returns to the low
end, the capacitor is good.
