Electricity For Refrigeration! Why Is LRA Important?

When discussing electricity for refrigeration and how it effects compressors, you must understand lock rotor amps (LRA). If you check the data plate on any refrigeration compressor you'll notice the LRA.

What does it mean?

The LRA indicates how much amperage the motor will pull while trying to make the rotor spin inside the stator, if the rotor is locked up!

What could caused it to lock up?

On reciprocating compressors, usually the crankshaft or a piston has broken.

So, what should you do when you have a compressor pulling LRA?

If the compressor is three phase, try reversing any two of the compressor leads.

What do I mean by reversing leads?

Take any two of the three wires and interchange them. Put the first wire where the second was and put the second wire where the first was. Reversing any two leads on a three phase motor causes the motor to change rotation. If the compressor is not "busted up" inside, but merely seized, it may start.

What could cause it to seize?

The most likely suspect is, lack of lubrication.

But that's another topic for discussion.

Also check the evaporator. Is it flooded with liquid refrigerant?

If the compressor still doesn't start after reversing leads?

You're going to have to inspect the crankcase and probably replace the compressor.

When your amp meter registers LRA, it's usually not good news for the customer!

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