Refrigeration Oil?
Dreaded Black Sight Glass?

Refrigeration oil sight glass black?

A first glance I thought the refrigeration compressor crankcase had no oil.

Shining my headlamp into the sight glass, I could see nothing. It was as if the light had disappeared.

But looking closer I began to see very small bubbles slowly rising.

I now knew what I was seeing. The dreaded black sight glass!


Why dread seeing a black sight glass?

It's a sure indication of a compressor burn out.

Burn out? A burn out means what it says. The compressor motor windings literally burn!

When this happens inside the compressor it creates a mess, an ugly, nasty mess.

The oil in the crankcase is sooty black. It smells terrible and becomes very acidic.

If you get it on your hands, wash them quickly!

What to do with a burn out?

The entire refrigeration system must be cleaned.

Over the years, I have tried many methods. The best way?

Simply change the oil. After the compressor runs, check and change it again. Keep changing until it returns to its virgin state.

How many times?

It depends upon the severity of the bunt out. A slight burn out requires few changes. A severe burn out can require many.

What about the filter driers?

Unless they are severely restricted I do not change them until the oil is clean.

Then I install new filter driers.

You could install a replaceable core drier and change them more often. But I think it is a waste of time.

The oil traveling through the refrigeration equipment slowly but surely "washes" the contamination back to the crankcase.

Before permanently placing the compressor into operation, do a refrigeration oil acid test.

Acid test kits are simple and quick.

Why not acid test as you change the oil?

The oil slowly returns to its virgin appearance. From black, to dark gray, to light gray, etc...

Until the last few changes it is too dirty to give you a proper color test comparison. It's a waste of time and kits.

Do I really dread seeing a black sight glass?

Not really. It's just one more tale the refrigeration oil tells. Just one more sign.

Ignore the black sight glass? Guarantee you the new compressor will not survive long! It put new meaning into the phrase "black death."



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