DWM Copeland... Help please?

[Mr-Frosty]

Firstly i will give you a run down of the job.

I attended the site of a deep freeze cold room on r404a there are 4 units and 4 evaps in this cold store.

i cant remember the model number of the compressor off hand it was a 6 cylinder model. anyways i dound the unit kept tripping on oil pressure so i reset the unit it ran for 90 seconds then cut off again. my suction pressure was 15 psi (roughly) as it didnt run for long enough and liquid was about 220 (roughly) the coldstore was at -19 set at -22 i checked my oil pressure and had between 25-30lb whilst the unit was running and the oil level looked a little low. there was oil coming back from the seperator so i pumped the system down a few times and i drained the oil from the system. i cleaned the oil filter and added 5 litres of fresh oil to the system. i ran the system again and exactly the same problem as before. i put the problem down to being a faulty oil pressure switch. i couldnt get hold of the oil switch due to suppliers out of stock through bad weather and minimal deliveries so my only option was to wire out the switch for the weekend (now thursday) so the customer was with full use of his coldstore. well we recieved a call out on sunday afternoon to this unit. when i arrived the flare had split on the sump from the oil seperatore and thrown the oil from the system and smashed the compressor to pieces. the pressure was the same on both hp lp sides and suction side was warm.

we managed to get hold of a re manufactured compressor and i fit it today. i completely re made the oil line as i thought it may have gone brittle i pressure tested the system fit a new oil pressure switch vacced the system for 24 hours and re charged. i clamped out the new compressor i was averaging about 14-15amps per phase one one set of windings and about 10 aps per phase on the second set of windings. i had oil pressure of about 50psi and the system seems to be working spot on including all safety cutouts. the oil line seems a tad warm to me and there is oil coming back to the compressor. id say at a guess the oil return is around 55 degrees C
i have a suction pressure of 15psi and liquid at 240psi

my questions are-
what could have caused the failure of the first compressor?
what could cause the rupture of the oil line?

id just like a few answers for piece of mind

thank you for your time

Mr-Frosty

[Mr-Frosty]

come on lads 30 views and not one reply. all advice greatly appreciated

[monkey spanners]

As a guess, oil seperator float letting by, compressor runs a bearing and starts vibrating badly, snaps of oil line. The difference in the oil pressures between original and replacement comps show something was wrong in the original imo.

Other thing to check is discharge non return valve as if it is faulty or now has bits of broken compressor in it, it may allow liquid to condense in the oil seperator and then return to the sump of the new comp.

Hopefully some others will comment who work on this size of equipment more than i do. Most of my stuff is sub 10hp.

[Mr-Frosty]

thank you for your reply monkey spanners as you can see i am new on here and the reason for joining was to try better myself and to also help others where possible. i thought the float from the oil sep sticking open could have been the cause i have given it abit of persuasion today but i also did the same when the old compressor was running. there does seem to be a big difference in the oil pressure between the 2 compressors. i cant get my head around it happening unless the float sticking was an intermittent fault.

[lowcool]

original oil pressure was low indicating compressor wear more than likely.wear maybe contributed to liquid flood back or migration.had a similar problem many moons ago another mechanic rolled up for a different call and found flood back caused by swarf intermittently holding llsv open.not bad considering instal was done donkeys years earlier,core drier and no obvious liquid line repairs.

such is life

[Mr-Frosty]

thank you for your comments i was back on site today and all seemed to be working fine. i checked the liq sol valve and it seems fine. i gues the compressor may have just been on its last legs. just an evap fan to sort now and touch wood the site is problem free. thanks for your help guys much appreciated

[glenn1340]

Maybe sods law coming into play...the flare nut splitting when the oil pressure switch was linked out, any other time and the switch would have done its job and shut down the compressor

[Mr-Frosty]

i think this was the case to be honest. i will be calling in over the next couple of days and keeping a close eye on the system as these compressors aint cheap.

[Mr-Frosty]

i recieved a call out today stating the oil line had been blown of from the sump yet again. what could be causing this as everything seemed to be running sweet i am now beating myself up over it as i cannot come to a conclusion???? any help appreciated

[Grizzly]

It may be a "red herring" as they say!

But this sticking oil return float that at a later date you gave a "little Persuasion"
May be the key, you say you recharged the system with 5 ltrs of oil.
Was that the compressor or the oil separator?

When the pipe split, oil from both the compressor and oil return lines / separator would of leaked out certainly until the oil float shut itself.
However, replacing the comp oil or indeed replacing the compressor with a new one would not replenish the oil in the separator.
This may just be one of the reasons for this latest failure, particularly if you have a oil float playing up.

What I am trying to say is you need to have a working level of oil in the separator as well as in the compressor.
I hope this helps?
Grizzly

[monkey spanners]

Is this a copper return line and could it be replace with a flexible line instead?

[Grizzly]

Is this a copper return line and could it be replace with a flexible line instead?

Yet another good point Jon.;)
I had not thought about stress fracture of the oil line.
Mr Frosty should have plenty to go on with.
Grizzly

[Mr-Frosty]

the compressor still works as it knocked off on safety.

the oil sep is a hermetic with a 1/4" line returning to the sump on the comp with solenoid and sight glass. when i charged the oil in the first compressor i charged it directly in to the compressor. i had a 3/4 full glass of oil on the compressor and also had oil returning from the oil sep. what i cant understand is what is causing the line to rupture?

my head is doing sommersaults over this now

[Mr-Frosty]

when i replaced the oil line i also put a few 6 inch loops into the line to help aid with any vibration and expnsion and contraction

[monkey spanners]

...just an evap fan to sort now...

Just a thought, if there is a bad evap fan on this system, you could be getting liquid back as the evap will have lost some air flow and hence the load will be lower, also unless the evap has baffles the other fans will pull air through the duff one as it is an easier path than through the coil, especially when it has some frost on it.
It depends on many things, not least how low a duty the txv is able to modulate down to, but the only way you will know for sure what is going on is to be there if it happens again. Its worth running it through a defrost etc just to see if anything odd happens in this mode too.

In the past i have had to disconnect evap fans but leave the system running, in this case i have blocked off the fan grill with a plastic lid off one of those catering sized food tubs till i could get a replacement.

[Mr-Frosty]

i have already removed the evap fan and have blocked off the opening in the cooler. the system is also ice free and runs through a defrost as normal. i have checked the load on the compressor also when i installed the new compressor. full load amps on the new comp was 18amp per phase and it was pulling 14amp per phase for the day i had it on test. i have replaced the oil line by brazing a schrader port onto the oil return line from the sight glass and removed the scrader and then fitted a flexible hose line back to the compressor. i will have to spend some time on site tomorrow to work out why this occured.