Question on oil pressure control wiring and possibility of compressor overhaulingl

[ventusfrigus]

Dear fellows:

Thank you for allowing me into your forum. This is my first post. I live and work in the Republic of Panama, a little country located in Central America. Just out of technical college and starting in the refrigeration business.
Last week I had to take care of a service call regarding a 15HP semi-hermetic Copeland compressor which was apparently running but not compressing. After removing the front plate (the one which holds the oil pump) I could see that all the crankshaft rods where gone: totally ruined. I took away one of the cylinder heads and saw a very scratched crankshaft. I can guess there was an oil circulation problem and the oil pressure control never tripped. First: what is the correct wiring for a typical oil pressure control (instructions show various ways of wiring them). Second: on site compressor overhauling is very common here, but how can you determine if a scratched crankshaft is repairable or just beyond repair?
Thanks for your responses.

[mbc]

all oil pressure have wiring diagrams you have to look at if you could not find go for new one or ask me to mail it to you ,
what is the your oil pressure type . various wiring for different voltage So choose right one for your voltage

about overheating it can be from different reason ,
if ---your system have a air -- your system over charge --- your condenser dirty or small--
some of old DWM compressor in low temp. needs to cool by fan --- expansion valve does not celebrate

[Grizzly]

welcome ventusfrigus.

If you can let us know what actual oil differential switch you have fitted.
Then I or others should be able to help you.
With regard to crankshaft wear?

Given you suspect the lubrication system has failed to the extent that the bearing journals have become scored and the con rods have failed.
I would normally suggest a crank regrind, however I don't know what options you actually have with regard to a Copeland comp? Nor what spares re oversize con rods are available?

I have in the past got away with light scoring, however yours does not sound like light scoring?
For that reason I would not recommend just rebuilding, unless the customer is prepared to take the risk at his cost.

It is often better to go that extra mile and have the crank reground. To give yourself that extra peace of mind.

You question the oil pressure safety control that's a relevant question. But have you considered that liquid flood back may have caused your damage?

Good luck Grizzly

[ventusfrigus]

Good evening and thank you very much for your responses.

1. The oil pressure safety control I have readily available is a RANCO model P30-3601. Apparently is a 60 seconds time delay model, with adjustable differential pressure setting.
It has dual voltage capability (120/240V). I can see three terminals marked "L", "M", and "A" in the time delay module, and two terminals in the differential pressure switch. Instructions offer at least three wiring options which in my case makes me doubt about the one I should apply in this case or in any other.

2. Since the compressor had already failed before I arrived, I do not have much information on the differential pressure readings before the damage. I think I have read that Copeland compressors require at least 11 psig of differential net pressure in order to assure correct oil supply to the bearings and crankshaft rods.

3. Aftermarket Copeland parts are readily available down here. They even have both crankshaft rods and bearing sets oversized ( they appear in the catalog as 0.020 and 0.010) in order to be used with rectified crankshafts. But I still don´t know if the scratched crankshaft is beyond repairing level, I mean if it can still be fitted with any of the oversized rods and bearings. What should be a good tolerance between the crankshaft and the rods/bearing ?

4. One thing I did notice is that suction reeds, discharge valves and valve plates, and even the cylinder tops where not damaged or scored. I guess that could be an indication suggesting that liquid slugging was not present, but I cannot be sure. Other interesting point is that not one of the rods survived: all were broken and lying in pieces on the crankcase, as if the damage had ocurred simultaneously in all of them.

[D.D.KORANNE]

1.0 oil return could be another issue that you will have look into..
1.1 if oil separator is installed , check it`s function
1.2 oil pump uptake filter clogging

tex valve setting ...... To be checked .........these issues need to addressed to avoid recurring failure ....

[Grizzly]

Hi ventusfrigus.

below is the details of how to connect your ranco oil pressure switch.
Personally I still suspect that this machine has had liquid carry over.
You say it was running but not compressing. We know why it was not compressing.
That sort of damage would not just be from running out of oil pressure.
If that was the case your Crankshaft journals would of picked up. or at least have some discolouration.
The stresses and strains on the con rods does not have to be from one event.
For all you know they may have been progressively weakened over time.
Not all the con rods have to fail at once either!
As long as oil is being pumped through the crankshaft with the required back pressure
the comp will run.
I have actually seen a small recip run so smooth that you could stand a 50p coin (Flat sided) on the body, without it falling over.
When stripped it had nothing left of the con rods they were all in bits in the sump.

I cannot advise at present as to the regrind values. But a rebuild company would know.
I still think you are to easily discounting the liquid carry over.
If the comp was running as you say then you would not have any evidence of carry over.
Have you checked to see if your crankcase heater is still working?

Grizzly


http://i851.photobucket.com/albums/ab77/grizzlysj/RancoP30pressureswitchOil.jpg

[mrfix]

I have found people putting a jumper wire between L and M effectively disabling the oil control. To test the control after checking the wiring take a small screw driver and carefully pry up the diff switch for the 2 min. and it should shut down the compressor.

[sedgy]

hi ,
the quickest way to test the oil pumps switch is to isolate the 3 ph to the comp, turn on to < run <
now with there being no pressure for more than 90 seconds the internal heater will trip out the oil pump switch, hope this helps , sedgy.

[ventusfrigus]

Hi fellows, happiest New Year to all, and thank you for your responses.
I went this morning to the local Copeland dealer, and asked for some information on recommended differential oil pressure controls. I was offered a Johnson Controls P445 electronic control which works with a special sensor to be installed in a round port located in the Discus oil pump. Is any of you familiar with this control ? Would it be a safer option than the regular electromechanical device similar to the Ranco control I mentioned before.