What happens if oil level is above 3/4 of sight glass???

[georgedvf]

Hello everyone!!

I've seen that reciprocating compressors manufacturers recomend the oil charge to be at 3/4 of the sight glass level.

What happens if someone charges more oil and gets above the 3/4 of the sigh glass level???

Or even worse, what happens if someone charges twice the required amount of oil???

I've been told that a compressor that has been overload with oil would overheat and protect himself by thermal protection over and over...

[Brian_UK]

If you overcharge with oil and have a high oil level then it is possible to destroy the compressor with liquid slugging.

[georgedvf]

Any idea why the compressor I mentioned in the first post could be protecting itself?

If there's oil overcharge, but not enough to break the compressor on liquid slugging, is it possible that it just run under harder conditions and overcurrent protection cut out the compressor?

[Sandro Baptista]

I don't think so.

My idea is the oil will be not still maybe be will be foaming...the dirt will not seattle down on the crankcase and maybe lubricating problems will occur.

[sendhilkmar]

If the oil has been overcharged then compressor likely to take high current and trips on OLP. Also you can see more oil in the evaporator and capillary/TXV that affects the system performance.

[NoNickName]

Too much oil would cause oil to foam up and being carried over to the system.

Manufacturer charge 3/4, because some of it will grease the piping and will remain trapped on the circuit.

[georgedvf]

I don't think so.

My idea is the oil will be not still maybe be will be foaming...the dirt will not seattle down on the crankcase and maybe lubricating problems will occur.

Sandro Baptista: if there's lubricating problems (not big enough to break the compressor) isn't there high current?

Too much oil would cause oil to foam up and being carried over to the system.

Manufacturer charge 3/4, because some of it will grease the piping and will remain trapped on the circuit.

NoNickName: do you mean all the oil will foam up??
If the oil is carried over the system it means the compressor runs out of oil, meaning lubricating problems, meaning high current, meaning overload trip, am I right?

[TRASH101]

Maybe a lot of oil has carried into to the evaporator/ or clogged the expansion device and is causing the superheat to climb which will cause the compressor to get hotter.

Maybe we need more details of the system to help you better.

[NoNickName]

NoNickName: do you mean all the oil will foam up??

No, I mean the excessive oil will foam the same way egg whites are whisked when agitated in a mixer.
Oil shall never touch the big end of the rod and the crankshaft, otherwise whisking happens.

If the oil is carried over the system it means the compressor runs out of oil, meaning lubricating problems, meaning high current, meaning overload trip, am I right?

No. You are drawing conclusions based on your conviction.
As long as the mass flow of oil leaving the compressor equates the mass flow entering the compressor, there is no possibility of dry run, irrespective of the initial oil quantity.
The mass flow, on the other hand, is enhanced by the amount of foam, which in the end is proportional to the oil charge.

As I see it, there is little to no relationship between oil amount and compressor overload.

[chemi-cool]

To make a long story short, take out the excessive oil.

This way you will be on the safe side.

[Grizzly]

Sorry nonickname, I don't really agree with your assessment.
I may be wrong but the way I see it is :-
Insufficient clearance within the crankcase due to high oil level.
Added to any hydraulic effects caused would create a motor overload scenario.
With a high enough oil level the recip compressor will become a very effective oil pump.
But moving a liquid requires much more energy than moving a gas.
As others suggest just bleed off the excess oil.
Grizzly

[NoNickName]

Surely, the extra oil causes extra work on the compressor. I wrote it.
That doesn't necessarily causes overload. In my view, there is no direct relationship between oil amount and overload, as not all of the overfilled compressors trip by overload.
In doubt, I agree that the extra oil is just a nuisance, and remove it will make no harm, and will actually do good. But again, I suspect, and I will be happy to be contradicted, that after having removed the extra oil, overload will still be happening.

[Grizzly]

that after having removed the extra oil, overload will still be happening.

Hopefully georgedvf will advise us of the outcome?
Grizzly

[georgedvf]

Unfortunately this was not a project of mine. A friend told me about it. The client decided to change the compressor without checking anything (what people do when have money)... so we'll never know if oil overcharge was the cause for OLP tripping.

Regards and thanks to all!

[NoNickName]

Good choice. Plenty of time for forensics later.