Congo Copeland advice

[George Askew]

13 Nov 08

Hi all.
Remember me? I`m the old S African Refrig Eng dragged out of ‘retirement’ to look after 4 systems in the Congo – after being out of the trade since 1965 [Except for a 10 day “refresher course” in Jan this year. So I am out of touch with some things but although I still remember quite a lot [Esp about the principles] , some of the controls and modern things etc leave me a bit baffled.

Here’s a situation I`d like some advice on please:

We have got a used old [15- 20 yrs] DWM Copeland 7.5hp compressor on a Viegra ice machine – and have had trouble with it since we got it. [See pix]

It had been standing for a long time and lost its gas, (R22), so hooked it up and started it. It ran OK for a few seconds then made an awful racket for a few seconds before I switched it off.
I waited a while and restarted it. It ran a bit longer before clattering away, and I cut it again – then I started it again – and so on.
This happened a few times with each time the running time getting longer and longer and the clattering getting shorter and shorter.

After about 6 “runs” I made a long distance cell call to S Africa to speak to the man who sold us the unit [a very experienced man with his own refrig Co] to discuss it. He was baffled and said to try and get refrigerant into it quickly – which was what I was doing – and within a few minutes of the same cycles the noise went away completely.
The machine has run intermittently over the last few months with no trouble from the compressor except for the occasional ‘clunk’ which puzzled me [One opinion I got was that it might be surges of liquid – but it also happened without the frostline being at the compressor. The bearings and piston sounded fine [using a screwdriver stethoscope]

It has however tripped a few times when running normally and after re-setting the relay it carried on fine – but puzzling.
And it also has been making ‘clunking’ sounds every so often – sometimes just 1 clunk, sometimes several, then OK and more so just lately.
Another thing that puzzled me was that the gauges were giving “wrong” readings [See pix] and comments below to the guy who sold us the unit.

• I phoned your dad today as I couldn’t get you about the noise the compressor was making on start-up. I had the gas bottle [R22] open and was filling the comp when a horrible shrieking metallic sound started. I switched the unit off. A few minutes later to try and establish the noise I started it again. This time it ran fine for a few seconds then the terrible noise again. I checked the oils – sight glass just over ½ way and opened the port on the oil pump at the end of the compressor. A good strong stream of hot oil came out but it smelt slightly carbonized and was more dark than light colour. Switched off. I repeated this process about 6 times and every time the good proper running noise lasted longer and longer and the noise later and later. I closed the suction and ran it and that seemed to help. Putting some more gas in seemed to help then the noise went away.
• I kept charging with gas but the sight glass never seemed to fill. It never became clear – one could always see a current running through it and yet I poured in a whole cylinder of gas – even when it was frosting back to the compressor. [I subsequently took a lot of gas out of it again].
• And the pressures are puzzling. Suction is 1.9 and head 14. Why would suction be high and head low?

A few days ago when pumping down the system to service and check the expansion valves - the gauge just wouldn’t come down to just above zero and at .5Bar the compressor tripped.
It was quite hot so I assumed it must have tripped on thermal overload, so left it a few minutes until I felt it had cooled a bit and reset the relay and it ran for about 1 minute then cut out but when it tripped the second time I realised the unit was at trip heat again - so I figured that the overload was functioning fine.

Here are my questions.

If the unit tripped on thermal surely it would do this long before the heat became excessive and caused damage?
If it was over-hot then surely I would not be able to reset the relay it would just stay tripped. Yes or No?
If the relay could be reset would this indicate that the motor had cooled down sufficiently to not trip?

When we came to start it today it would run for from ½ a min to 1 min and then trip.

To me it was an electrical problem so got our electro to look at it.
He checked the external contacts and said he suspected something was wrong in the windings and so we opened the end cover to expose the armature.
The oil was disgusting – black and dirty with what looked like old worn metal dust in it.
The tape on the windings was as hard as rock and there was a small area of windings that looked suspect.
His theory is that the problem had been in existence a long time and that the oil had been acting as an insulation but occasionally failed and would short out.
He said “Mr George this machine has been sick for a long time but today its death day has come”.
This made sense to me as it could mean that the ‘clunking’ noises we used to hear were when the one wire shorted out briefly at times.

So would my resetting the relay and letting it run again when it was till hot [See above] make the problem worse and render the unit un-usable?

Would fine metal grindings in the old oil be responsible for the clunking?
Have I screwed up and caused the ‘Death’ by resetting it or was it just bad timing?

I am sure that the overheating was “The final nail in the coffin” and that the machine would not have functioned correctly even if the reset button had not been hit.

A local techie says that we cant rewind the stator [which to me is total BS] I used to strip service and reassemble hundreds of these as an Appy but that was back in the 50s and I have forgotten exactly how to remove the rotor and stator. To me it looks like we will need special tools [which we cant buy here and anyway would probably never use again] – So in view of no workshop of our own [we can get certain engineering down here tho], and with just some basic tools how do I remove these items?

FLUSHING
Please bear in mind we are really in the back of beyond and everything has to be flown in at great expense, inconvenience, and delay.
I cant allow the unit to be re-commissioned with all this bad oil and crap in it, and althoI have read of some recommended methods on this site they all are geared to where you can pop down the road and get what you want.
If I want a thorough flush do I need to dismantle most parts of the system – like receiver, condenser, evap, oil collector and cold gas “vessels” [Whatever they are called]. I would think so otherwise how does one get all the crap out with all the nice hiding places on the system.
Can I use steam – and then much evacuating / HP air and if so what pressure?
I am also having huge problems trying to get online so may not be able to respond to anyone who needs more info in a hurry.


Your comments please

I will be lapping in the reed valves as I believe they are the reason the unit would not pull down to 0. And on inspection they look like they need doing.
Regards
George

[George Askew]

How do I attach pix?

George A

[Toosh]

How do I attach pix?

George A

Hi George, go to top of page on the left you will see user cp click on it and scroll to bottom and you will see attachments

Norm

[George Askew]

Hi. Anybody out there?
I really need advice ASAP

George Askew

[George Askew]

Thanks Norm
G

[nike123]

It had been standing for a long time and lost its gas, (R22), so hooked it up and started it. It ran OK for a few seconds then made an awful racket for a few seconds before I switched it off.
I waited a while and restarted it. It ran a bit longer before clattering away, and I cut it again – then I started it again – and so on.
This happened a few times with each time the running time getting longer and longer and the clattering getting shorter and shorter.

After about 6 “runs” I made a long distance cell call to S Africa to speak to the man who sold us the unit [a very experienced man with his own refrig Co] to discuss it. He was baffled and said to try and get refrigerant into it quickly – which was what I was doing – and within a few minutes of the same cycles the noise went away completely.

I think what you are experiencing here is rattling of low pressure switch with automatic reset. That causes rattling of compressor contactor and "awful racket".

The machine has run intermittently over the last few months with no trouble from the compressor except for the occasional ‘clunk’ which puzzled me [One opinion I got was that it might be surges of liquid – but it also happened without the frostline being at the compressor. The bearings and piston sounded fine [using a screwdriver stethoscope]

It has however tripped a few times when running normally and after re-setting the relay it carried on fine – but puzzling.
And it also has been making ‘clunking’ sounds every so often – sometimes just 1 clunk, sometimes several, then OK and more so just lately.

Probably liquid flood back.

And the pressures are puzzling. Suction is 1.9 and head 14. Why would suction be high and head low?

Worn compressor.

A few days ago when pumping down the system to service and check the expansion valves - the gauge just wouldn’t come down to just above zero and at .5Bar the compressor tripped.
It was quite hot so I assumed it must have tripped on thermal overload, so left it a few minutes until I felt it had cooled a bit and reset the relay and it ran for about 1 minute then cut out but when it tripped the second time I realised the unit was at trip heat again - so I figured that the overload was functioning fine.

Here are my questions.

If the unit tripped on thermal surely it would do this long before the heat became excessive and caused damage?
If it was over-hot then surely I would not be able to reset the relay it would just stay tripped. Yes or No?

Thermal overload cannot sense internal winding temperature. For that you need Kriwan or simmilar product with PTC sensors.

Most likely is, that with high suction temperatures you have high current draw and thermal (over current) relay has tripped because of that. Therefore you are able to reset it very quickly.

If the relay could be reset would this indicate that the motor had cooled down sufficiently to not trip?

Over current thermal relay has nothing to sense compressor winding. It is called thermal because it works on principle of heating of his contacts by passing current and that way sensing excessive draw of current of compressor


Check 1st page here.

So would my resetting the relay and letting it run again when it was till hot [See above] make the problem worse and render the unit un-usable?

Yes! You should measure current draw and pressures to establish cause of tripping.

Would fine metal grindings in the old oil be responsible for the clunking?

Most likely NO!

Have I screwed up and caused the ‘Death’ by resetting it or was it just bad timing?

Bad timing! He was already worn.

I am sure that the overheating was “The final nail in the coffin” and that the machine would not have functioned correctly even if the reset button had not been hit.

If he was worn, he overheats from some consequent time before that event.

A local techie says that we cant rewind the stator [which to me is total BS] I used to strip service and reassemble hundreds of these as an Appy but that was back in the 50s and I have forgotten exactly how to remove the rotor and stator. To me it looks like we will need special tools [which we cant buy here and anyway would probably never use again] – So in view of no workshop of our own [we can get certain engineering down here tho], and with just some basic tools how do I remove these items?

It should be inspected for wear before deciding about rewinding.

[George Askew]

Hi Nike 123
Many thanks Amigo.
Where are you from and where are you based?

George

[nike123]

Hi Nike 123
Many thanks Amigo.
Where are you from and where are you based?

George

http://www.refrigeration-engineer.co...er.php?u=13885

[tonyelian]

hi georges
i think that u have a valves problem &that is happend cause u did not the proper job after long stop u should take the valve cover out &remove black sludge coming from long stop the oil became very attractive for humidity oil became black from the small particules devellopped on compressor parts crank rotor valves so i think a damage had happen to the valves &suction-pressure mixed together in valve plate causing pull down&heat problem
best regards &good luck

[George Askew]

Thanks Tonyelian
Didnt know that.
Actually I`m quite amazed at how complicated this industry has got in 37 years.