e-refrigeration.com

Compressor Faults

Some compressor manufacturers state that a high percent of the compressors that are returned to them have no faults.   

If you find that the compressor is not running or you hear the telltale "clicking sound" of the overload, then you need to check the start components as well as the compressor motor windings to determine the source of the problem.

Locked Motor

LRA = Locked Rotor Amperes. This represents the amperage if the rotor is prevented from turning. It also represents the amperage the motor will draw for a tiny fraction of a second when it is starting. It represents the maximum current your compressor will draw when seized but still drawing current (imagine someone throwing a spanner into the spokes of a motor).

If you get a reading that is either at or near that number, then it is likely that the compressor is locked up and needs to be replaced. If the reading is approximately half of the LRA it is very unlikely to be a Locked motor.

Start Component Test

Unplug or disconnect all electrical supply to the system and begin to remove the cover that holds the compressor start relay and overload.

Disconnect all of the start components from the compressor terminals. Use a multi meter to check the resistance of the compressor windings. 

There are three compressor windings and they are arranged in a pyramid shape. 

The majority of compressors have the top terminal of the compressor as common, the left is the start winding and right is the run winding.

You will need to test for resistance in these windings. Connect one probe of your multi meter to the start and one to the common terminal.  A resistance reading should be measured by your multi meter.

While all makes of compressors have variation in resistance readings generally what you need to know is that there is resistance there.

Then remove the probe from the run winding and connect it to the start winding. Again there should be a resistance reading. If either of these tests shows no resistance, then the compressor motor is faulty.

Grounded Motor Windings 

Another test to check for is for grounded windings. Set your multi meter to the highest resistance scale and press one probe to any of the winding terminals and the other probe to one of the copper lines or condenser coil. You may have to scratch the surface of the metal to make sure that you get a good connection.  If you get a reading the compressor is damaged.

It must be realised that if any of the above problems occur, sometimed the most cost effective way of solving it is to replace the refrigeration system, or just to replace the compressor itself.