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Inverter or Compressor: Which is the Culprit?

Son of Samurai

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VFD (Variable Frequency Drive) systems have been around long enough now that most of us know the procedure for troubleshooting them. You have three main tests that you perform:

1. Check for the PWM (Pulse Width Modulated) signal from the main control to the inverter. This is a DC square wave data signal that alternates between 0-5 VDC. The inverter has to receive this signal from the main board in order for it to run the motor.

2. Check the 120 VAC input to the inverter board. This has to be present for the inverter to do its job.

3. Check the resistance of the BLDC motor's windings. The exact reading can vary from motor to motor, but the important thing is that the windings' resistances be very close to one another -- within a 10th of an ohm.

If the inverter is receiving both of its inputs and the motor windings are in spec, you can usually safely conclude that you have a failed inverter.

Unless...

What if you're dealing with a BLDC compressor that has failed mechanically rather than electrically, meaning that the windings measure in spec, but the compressor is mechanically jammed? The inverter will be doing its best to run the compressor, but it simply can't. How do you avoid the false diagnosis of a failed inverter?

The esteemed Brother @EthanRanft has the answer. As he put it:

Quote

The last step [in your troubleshooting] would be to check amperage on the 120VAC supply to the inverter. If you disconnect power to the inverter, and then reconnect, a functioning inverter will try to start the compressor and you’ll see a few amps. If you’re seeing amperage on and off and the compressor isn’t starting, you know the compressor is locked. LR amps on an inverter compressor is only about 4A

There you have it -- one simple amp measurement tells you if the inverter is doing its job! That's one more tidbit to add to your mental toolbox...

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jcraig9218

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How about some input on the LG linear compressors? The ones with continuity on only two of the three connection pins. How do you test them? Is there a way to use some kind of a starter? One LG video shows one they call a jig but no explanation or wiring diagram.

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Son of Samurai

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2 hours ago, jcraig9218 said:

How about some input on the LG linear compressors? The ones with continuity on only two of the three connection pins. How do you test them? Is there a way to use some kind of a starter? One LG video shows one they call a jig but no explanation or wiring diagram.

This particular blog post was about BLDC compressors, but this is a great question about linear compressors! We have a webinar recording that takes a deep dive into both linear compressors and linear motors.

Access to webinar recordings is one of many features available to techs with Professional Appliantologist memberships. Professional Appliantologists support this site both financially and with their helpful input on topics, so in return they get a whole range of goodies to help them in the craft, including access to webinar recordings. 

The Webinar Recordings page is an archive of all of the past webinars the Samurai has hosted. There’s hours of material there. Each recording is a detailed look at a specific technology or troubleshooting strategy. Techs of any experience can sharpen their skills by watching these recordings.

And that's just one of many benefits of becoming a premium member! If you are interested in becoming a Professional Appliantologist and getting these goodies for yourself, click below.

 

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jcraig9218

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Thanks for the response and the link to the webinar I need. However, it says I'm not authorized although I have taken Fundamentals and Refrigeration courses. Please advise. Thanks!

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11 hours ago, jcraig9218 said:

However, it says I'm not authorized although I have taken Fundamentals and Refrigeration courses.

You did have a free premium Alumnus membership previously. However, that membership has a forum activity requirement that you did not meet (more info on that here: https://appliantology.org/blogs/entry/1005-the-master-samurai-tech-alumni-program/).

If you would like to regain premium access to Appliantology, which includes the ability to watch webinar recordings, you can consider becoming a Professional Appliantologist member here:

 

 

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