Overload Protector; Ptc Starter - EdgeStar CWB8420DZ Service Manual

9.4.7 Overload Protector

The overload protector prevents the compressor from burning out its electrical windings in the
event the compressor becomes overheated or draws too much current. The overload trips,
opening the circuit to the compressor. If it does this repeatedly, the compressor is said to be
cycling on the overload. Cycling on the overload may be caused by:
1. Insufficient air circulation around the compressor and condenser.
2. Pull-down on the compressor, caused by a large quantity of warm food or beverages
placed in the refrigerator.
3. Compressor stalling due to lack of pressure unloading.
4. Low line voltage.
5. Defective start relay.
6. Defective winding in the compressor or shorted windings.
Testing the Overload Protector
Disconnect the unit from power. To test the overload protector (OLP), remove the compressor
terminal cover. Examine the bottom of the OLP for signs of arcing. If signs of arcing are
present, either check for continuity or connect a jumper wire across the terminals. If using a
jumper wire, plug in the line cord and set the temperature control to a cold setting. If the
compressor starts, the OLP is defective and must be replaced. If the compressor fails to start,
check for a defective start relay or compressor.
1. Remove the PTC starter and OLP from the compressor.
2. Connect one ohmmeter probe to the compressor shell. Make sure the probe makes good
contact with bare metal. One at a time, connect the other ohm-meter probe to each of the
three compressor terminals.
3. If the meter shows no continuity to ground, install PTC and overload protector to the
compressor's terminals. If the meter indicates the compressor terminals are grounded,
replace the compressor.
4. Attach a jumper wire across the OLP terminals.
5. Make sure the jumper wire does not short to ground.
6. Reconnect the unit to power source. If the compressor starts, the overload protector is
defective and must be re-placed.

9.4.8 PTC Starter

The PTC solid state starting device is a push-on component mounted to the start and run terminals
of the compressor. This device is connected in parallel with the run capacitor and is in series with
the compressor start windings. This will produce a short circuit across the run capacitor during
the compressor starting sequence and full current is applied to the start and main windings.
Since the PTC device is temperature sensitive, a variance in its temperature causes a change
in its resistance. When current is first applied to the compressor, the PTC device's low
resistance shorts out the run capacitor producing adequate motor starting torque. As the
compressor motor approaches running 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.