low temperature rack unbalance problem

[racktech2008]

Recently, I visited a ten-year-old low temperature rack system which includes three walk-in freezers. The problem reported by the owner was that only ONE of the freezers was working nicely (at -17 deg. C), while the other two were having problems keeping temperatures below -8 deg C. My supervisor suggested the possibility of a leak, but the situation didn´t improved with the addition of refrigerant. He then advised me to change all TXVs in one of the freezers. Results were very positive. He instructed me to repeat the same job in a second freezer, with similar results. I thought I was done with this, but now it seems that the only freezer which was working properly before we came here, IS THE ONE WITH THE WARMEST TEMPERATURE!!! . I guess I have screwed up the system balance. How can I re-balance this system: by changing the TXVs in the remaining freezer?

[mctavara]

Are these freezers conncted in a common main header? check the piping system. Maybe the main manifold need to resized

[750 Valve]

Could be heaps of reasons... you don't need to "balance them" they aren't like a water circuit, they just need to perform to their maximum capacity (design)

Firstly did you check the strainers in the old TXV's before you removed them? May not have needed to fit new TXVs - just clean strainers.

The txv's you fitted, were they the same or correct rated capacity for the coils? Did you check the superheat and adjust if necessary after fitting them?

What are the suction and discharge pressures? what refrigerant? commonly to achieve a -20C room temp you need approx -25C saturated suction temp and likely colder if you have glass door freezers (-30C) on the same rack and definitely colder for wide islands (-35C). Are there any EPRs fitted like ORIT or SORIT valves? if so what are their settings?

Poor condenser fan cycling can affect PD across valve if HP's are allowed to plummet or fluctuate massively, are the valves you fitted balanced port valves?

Have you checked for pressure drop between the coils and the comps at the rack? possibly clogged suction socks left in the rack for years.

start here, its all the usual stuff

[Peter_1]

....My supervisor suggested the possibility of a leak, but the situation didn´t improved with the addition of refrigerant. He then advised me to change all TXVs in one of the freezers. Results were very positive. He instructed me to repeat the same job in a second freezer, with similar results. I thought I was done with this, but now it seems that the only freezer which was working properly before we came here, IS THE ONE WITH THE WARMEST TEMPERATURE!!! . I guess I have screwed up the system balance. How can I re-balance this system: by changing the TXVs in the remaining freezer?

Your supervisor suggested to replace all the TXV's :confused::confused::eek:
Why he suggested that, based on what measurements?

And he also suggested to add refrigerant...was there a reason, or better..were the measurements of SH, SC, LP, HP,... in such a unbalance that could be decided that there was a shortage of gas anyway?

I should suggest to tell your supervisor if all this doesn't help, replace all the compressors.
If this doesn't help, say him you should change then the condensers too.
Finally, if even this doesn't help, change all the evaporators.

I repaired once this way a jet-engine on a B747 and also a CER scanner in a hospital.;)

[tony--1]

peter As site moderator i dont think taking the piss is very good. and no help to this guy just because his supervisor is dumb.

[tony--1]

racktech2008 has your supervisor been and had a look at this or is he trying to fix it on the phone ?

[Peter_1]

I'm not taking the piss - whatever this may be - on/for racktech2008.
He's not long in this trade and we all have to learn.
He's visiting this site for help and I'm not blaming him for anything nor joking with him personally.

It's his supervisor who needs more this forum then racktech2008 needs. His supervisor is not worth his title.

You have to agree with me that his supervisor hasn't a clue at all what he's talking about.
"Change a piece and look what's happening"

Racktech2008, now some good advice: you have to search what changed since the install. I suppose everything was fine till some weeks/months. So something has changed which provoked the malfunctions.
You have to find this.

Start by asking direct questions to the customer, try to rebuild the recent history of the rack, especially past problems.
Have other techs worked on this rack and what have they done?

Start with the rack: is it running with the right pressures and temperatures?
Is there enough gas in the system? Don't add gas if you're not sure that there's not sufficient gas in the system.

If you decided that the rack is running well, go then to the cabinets.
Start with your eyes: coil not under ice, frosted equally, all fans running, ...?
Measure SH at the outlet of the coil and measure liquid temperature at the inlet of the TEV (flashgas)

A TEV can be faulty but not all of them at a time. If you want to replace a TEV, then you have to analyze first by measuring temperatures and pressures if the TEV is faulty.

Hopes this helps more and don't listen to much any longer to your supervisor because he is more a DIY'er, a parts-replacer then a real tech.

[Chunk]

And always leave a logbook in the plantroom so that whenever an engineer does any work they can fill it in with date and description of work carried out.This will help not only you,but any engineer that attends.

This is also a good way to keep an eye on what actually goes on,and a record of what parts and how much gas is being used.

[tony--1]

Peter. that was my point his supervisor is probably trying to fix this job on the phone . instead of getting of his a** and going to site . my job title is supervisor and i would be to the site in a second to try and fix this with the engineer .

[Peter_1]

With all my respect for raktech2008 but he needs for such a job an experienced tech besides him to guide and help him, not to let him solve these problems alone.
He can't have enough experience at his age.

Unless racktech2008 and his supervisor are one and the same person :p

[750 Valve]

Even if the stuporvisor was advising this from the end of the phone in my opinion he is not worth a pinch of.... well lets just say he isn't a good fridgey.

A supervisor should be able to give adequate tech advice whether on site or on the end of a phone, that is supposedly why they are supervisors, they have experience and are able to pass this experience on to others.

Rather than say change all the txv's or add gas and see if it works he should be asking all the questions that we all have posed to racktech or perhaps, as peter suggests the supervisor should become a member here and do a bit of reading...

hang in there racktech and check the simple things first, be sure to get back to us and let us all know how you went

[Peter_1]

Yeah Racktech, and teach your supervisor yourself with the help of this community.

[IceMan08]

I'd check the tev's first-wrap a hot cloth round them-if gas 'whooshes' through you've got moisture in the system, would then require the system to be vacced out, but i guess its in a supermarket and they NEVER like to empty a cab! in which case change the dryer for new,pref oversized, keep heating the tevs to get the moisture out and into the dryer.Although it could various simpler answers. Peter 1,like your answer! I used to have a supervisor like that when i worked for a certain fridge company that these forums are filling up with rumours about.
I have several hilarious stories about him but its not the time, nor place!
It really does go to show, Its who you know not what you know!!!

[Peter_1]

Racktech, as 750Valve said, you can't balance a rack and the rack runs independent form the cabinets.
A rack simply maintains a preset LP and HP, that's all.

[abet_meneses]

Hi rack tech,a bit of advice before replacing TXV try to adjust 1st maybe it has high superheat.check superheat with press. gauge connected on suction line.observe ice formation on the after each calibration.also check condenser press,epr,thermostat control,drier before txv and last refrigerant level at the reciever.

[Gary]

Stop guessing at what might be wrong and figure it out.

[bill1983]

is the same rack you had a gas leak on last year around this time?