coffin slugging??

[mrfreeze666]

i have been working in this supermarket for a yr now,rack is r-22,5 compressors with sattelite on left which is just part of rack. been there numorous times for oil fail,line from coffin fosted so bad makes end bells to comp frosted which then covers entires comp including oil pump to make comp fail thus making sattelite to then ice over. i have been saying we need to address this and find which case or cases are doing this, well i was told to put in epr valve which i did, and still having trouble, was there recently and found oil washed out of usual comp,am i wrong to say problem is in 1 or more coffins or am i missing something. thers 20% in receiver, head pressure good and back pressure good. it seems they dont want to put time into cases to find problem, not sure if its my boss or company i work for.
any thoughts anyone would be appriciated

[captinsano]

Check your superheat on case in question also look around the area of that case and make sure there are no supply ducts from store A/C blowing in and disturbing air curtain on coffin case.you may want to go through and tune up all the cases that rack serves.It is probably something very simple being overlooked.

[icemeister]

Your company has a PM contract with this store that doesn't include replacement compressors.

[guy in blue van]

when you force coffins into defrost does the frost on the end bell go away? if so than open those coffins up and have a look. could be something very simple. what did you set your epr for? whats the t-stat set for? hows defrost operation? Im not sure if you should bother with looking for A/C killing air cutain if these cases have been working fine for the year that you have been in the store.but I would at least have them stip the case so you can rule out the easy stuff.this would also be a great time to start checkin superheat as the captain said.

let us know what you find. its always a pain in the arse to chase floodback

[guy in blue van]

hey mr. meister ya said that you ran the ref. dept. for edwards. what are you up to now?

[luvcldair]

They will want to put the time and $$$$ into it once the compressor take a crap...be sure to let them know it will void warranty of the problem isnt resolved if the compressor does go bad...

But on a serious note i would go throught superheats on the cases in question. also may want to make sure epr's arent set to low or ensure that they due shut down when they are suppose to....

[icemeister]

Originally posted by guy in blue van
hey mr. meister ya said that you ran the ref. dept. for edwards. what are you up to now?

I've been doing a one-man wrench-turnin' refer gig in Florida for 15 years now. It's almost like being semi-retired compared to the old rat race.

[frozensolid]

Clean the strainer and put on a vzp pressure limiting powerhead.

[iceman373]

is there anyway you can monitor loads on the cases. it sounds like a air flow and load demand issue. ie they fill the cases making a hot type pulldown, vapor density increases. customers empty cases unusally fast during latent heat transfers . Then the load demands change to fast causing vapor density to react almost as a restriction. End result is major frosting.,

[icemeister]

Originally posted by iceman373
is there anyway you can monitor loads on the cases?

Yes. It's called a properly sized, adjusted and maintained thermostatic expansion valve......like the one that should be in that case that's causing all the trouble.

[luvcldair]

Well said..........

[iceman373]

usally, there is a instore utilty mechanic that can help, or talk with the produce/frozen meats supervisior. they know whats coming in and whats on sale and where its going days in advance., If its a large chain, they even know where and how they are going to display it weeks in advance.

[iceman373]

assuming that proper superheat and subcooling is not in disaray.

[thegoodhumorman]

I wouold add its worth noting that if the liquid line runs inside the cases you will be receiving some killer subcooling on liquid to case txvs at furthest end and those valves should be pinched down moreso than the others for this reason. Either way you slice it, you need to spend some serious time on superheats.
theres also possibility that an internally cracked heat exchanger in case present.

Nothing worse than changing a compressor where you knew that it was coming but you didnt prevent it. If you are drawing a blank then do your company favor by advising that theres obviously a problem and send out someone else.

If the customer doesnt want to pay the labor - hey its on him and you can snigger when the dread reaper comes to collect that anchor....

[Edited by thegoodhumorman on 02-26-2006 at 05:17 PM]

[thegoodhumorman]

It only takes one TXV flooding to do this- could be more
but-
somebody is paying a lot for your company to drive there to reset compressor. Sounds like a Safeway contract....

[razorback]

[QUOTE]theres also possibility that an internally cracked heat exchanger in case present.[QUOTE]

Flooding that bad on a rack this is where I would start. But if nobody cares( until it breaks ), changing compressors is good experience- especially on nights and weekends.

[badbillr]

if the end bells are frosting over, you WILL be replacing or re-building a compressor in the near future. been to a couple of carrier's semi-hermetic classes. the one thing they constantly keep telling & showing pictures of is a compressor gone bad due to liquid refrigerant returning back to the compressor. even if the bell ends loose the frost after a defrost cycle, i bet there is a ton of liquid refrigerant trapped in the compressor oil.

you seriously need to take superheat readings & sub-cooling readings. with this info, you should be able to present these facts to your boss to prove to him the system is flooding back & needs to be address. i like the idea of installing a pressure limiting txv . make sure the sensing bulb is positioned correctly, tight to the pipe and is insulated properly.

[shaun66]

one compressor icing over or whole rack? HG defrost? check valve dinked?