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Rigging and using a compressor test cord to manually operate a compressor

Samurai Appliance Repair Man

5,901 views

One of the many things that can make a refrigerator warm up is the compressor is trying but failing to start. You may occasionally hear this type of noise from the back of the refrigerator (starts about 15 seconds in):

This is the sound of your compressor trying, but failing miserably, to start. Best case scenario: Bad compressor start relay. Worst case scenario: open compressor start winding or seized compressor bearing == buy a new refrigerator.

Question: How do you tell which is which?

Answer: Compressor test cord.

Question: What's a compressor test cord and how do I make one?

Answer:

gallery_4_4_7957.png

Question: How do you know which is the start, run, and common connection posts on the compressor?

Answer: Use Brother Bobice's procedure for identifying the compressor electrical terminals:

Using a good multimeter set on ohms, remove the compressor terminal cover with the unit off.

Touch one lead (of the meter) to one terminal and the other lead (of the meter) to one other terminal and record your reading . Lets call these terminals (A) and (B). The remaining terminal lets call ©

So for example A-B=7 Ohms

Now lets read A-C and record. Lets say 5 Ohms

Now lets read C-B and record. Lets say 12 Ohms

Now lets add all the A’s= 12 Ohms

Now lets add all the B’s=19 Ohms

Now lets add all the C’s=17 Ohms

The highest reading will be the “Start” winding

The next highest reading will be the “Run” winding

The lowest reading will be the “Common” winding

Therefore B= “Start”

The next is C=”Run”

The remaining terminal A= “Common”




8 Comments


DurhamAppliance

Posted

Just a reminder: Never ever introduce 120v directly to an inverter compressor. Ie if you don't see a start relay, don't use a test cord.

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I have a direct devise i got from G.E 30 years ago make by ROBINAIR that iforgot to give back to them 30 YEARS ago and its made just like your diagram.Comes very handy.

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I made one several years ago and it has really helped me. Looks like I won't be using it much in the future though.

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Why in the described testing procedure in steps 3 and 4 your resistance R to C equals S to C. Shouldn't S to C be much higher then R to C?

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Samurai Appliance Repair Man

Posted

Could you please be more specific about what you're referring to as steps 3 and 4?

 

I actually teach a much simpler method in the Refrigerators course. Stick with the method taught there.

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A couple of questions on the compressor cord. Should The circuit breaker fuse be 15 A? And is it on the neutral wire ? How many Mississippi's do I count on a momentary switch?

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Samurai Appliance Repair Man

Posted

A couple of questions on the compressor cord. Should The circuit breaker fuse be 15 A? And is it on the neutral wire ? How many Mississippi's do I count on a momentary switch?

 

Fuses and circuit breakers are there to protect the wires. So whatever size fuse you use, you should make sure the wire has sufficient ampacity. The NEC publishes ampacity tables like this one:

 

simple-ampacity-table.jpg

 

Doesn't matter if the fuse is in Line or Neutral because the current is same throughout the circuit. 

 

A good compressor will start up in less than one Mississippi. If you have to hold the start button closed for more than two Mississippi, the compressor is toast. 

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