Cool Room Evap Icing Up

Hi all, hope every one is well. I recently when to a job at a supermarket which has a compressor rack system with 4 compressors. Basically everything in the supermarket runs off the same system.

There is a cool room in there which is set to 4 degrees but it wont pull down to temperature and just sits at around 7 degrees and after about a day just ices up.
It has two evaporators running off the one solenoid and only one of the evaps totally ices up.

You can hear the solenoid opening and closing when you set the thermostat so that seems all fine. I changed and TXV on the evap that was icing up and now the solenoid valve. But then I set it back down to temp and it just ices up again. Could it be the TXV on the other unit? Im not sure what else to check. Fairly newbie at this game by the way. Appreciate any input!

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Short of refrigerant?

Rob

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So you checked the superheat on both evaps?
Assuming this system also is used for freezers, does the suction pressure regulator for these evaps operate OK?
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No it only operates for all the display cases and cool rooms, no freezers. Yeah the superheat is pretty much identical on both evaps. I know this sounds general but my company has been working on this system for about 10 years and whenever it is short on refrigerant exactly the same display case warms up first. Also everything else in the whole shop runs fine and cycles on temperature. Not a low refrigerant issue.
Not sure if this helps but the unit that doesnt ice up builds a bit of frost from the TXV body along the distributor lines whereas the one that totally ices up only begins at the distributor line and th body doesnt ice up.

From the sounds of things, I question the design.

Why have 2 evaporators, 2 TXVs and 1 liquid line solenoid. How are you controlling defrost?

How can 1 evaporator go into a defrost while the other one stays running? It couldn't happen as you would have a call for cooling (liquid solenoid open) and a call for defrost! You would certainly ice up the coil!

Do both evaporators defrost at the same time?

How old is this system? Any recent changes?

Attachment 11090

This diagram shows individual thermostats for individual rooms. Your application would require individual defrost time clocks on each evaporator with 2 independent liquid line solenoids utilizing 1 thermostats.

It doesnt have a defrost cycle on it. When it gets down to temp the fans just keep running. The problem is something is causing the room to not pull down to temperature and then the evap ices up. The ony way to defrost it is to put the temperature up so it stays cu tout on temperature. Then after I do that. I set it back to 4 degrees come back like 7 hours later, the temperature is sitting on 8 degrees or more and one of the evaps is totally iced up.

It is also a very old system and nothing has been changed recently.

Think I would check door seals,dirty evaporator faulty thermostat,s sensor/bulb location could you not put a multichannel temperature recorder in to see what's going on?,maybe a load issue,I have seen baldly designed equipment work fine for years did do not think that it's worked great but now faulty.

Evaporator has to be 100% clean to eliminate poor air flow as well.
You need to physically look at it.
Also check charge , infiltration like above posts state.

Then se what happens

Cheers guys, am going back in the morning to suss it out. definetely have a couple more things to check now. One quick question, Is it odd for one of the evaporators to totally ice up yet the other one that is maybe 3 metres to its left to not frost up at all even though they are exactly the same and both run off the same LLS and t/stat?

2 single phase fans in 1 evaporator? Baffle between both? No? Capacitor faulty on 1 fan, 1 spinning CW, the other CCW where you think both are running fine but no flow over the coil. Feel once in front of the coil.

Door open? No, then you should face same problems with the other one too.

Or, the faulty one takes his liquid on top of the liquid line. But then, these problems should happened already in the past.

Quote:

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Originally Posted by Peter_1

2 singel phase fans in 1 evaporator? Baffle between both? No? Capacitor faulty on 1 fan, 1 spinning CW, the other CCW where you think both are running fine but no flow over the coil. Feel once in front of the coil.

Door open? No, then you should face same problems with the other one too.

Or, the faulty one takes his liquid on top of the liquid line. But then, these problems should happened already in the past.

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Thanks mate. Yeah 3 single phase fans per evap. Saw them spinning but yeah I will check that to. Thanks so much for replying.

Something else to check is that the drain is clear, have seen icing problems where the condensate couldn't get away.

QUOTED: Not sure if this helps but the unit that doesnt ice up builds a bit of frost from the TXV body along the distributor lines whereas the one that totally ices up only begins at the distributor line and th body doesnt ice up.
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Iced up evaporator is carrying all the load. Room can't get to temperature so no off cycle to clear evap of frost. The other evap has valve or orifice trouble.

Quote:

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Originally Posted by mikeref

QUOTED: Not sure if this helps but the unit that doesnt ice up builds a bit of frost from the TXV body along the distributor lines whereas the one that totally ices up only begins at the distributor line and th body doesnt ice up.
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Iced up evaporator is carrying all the load. Room can't get to temperature so no off cycle to clear evap of frost. The other evap has valve or orifice trouble.

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Hit the nail on the head. I should have thought of this as I changed TXV and orifice on evap that was icing up, stupid in hindsight. Changed orifice on the other one today and bang unit hasnt missed a beat. Thanks mike and everyone else!

Quote:

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Originally Posted by stoljc05

No it only operates for all the display cases and cool rooms, no freezers. Yeah the superheat is pretty much identical on both evaps. I know this sounds general but my company has been working on this system for about 10 years and whenever it is short on refrigerant exactly the same display case warms up first. Also everything else in the whole shop runs fine and cycles on temperature. Not a low refrigerant issue.
Not sure if this helps but the unit that doesnt ice up builds a bit of frost from the TXV body along the distributor lines whereas the one that totally ices up only begins at the distributor line and th body doesnt ice up.

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Mike refs good pickup

So are we saying the superheat was OK but unit with little ice not performing!

Maybe in hindsight we should have asked for air on/off on Evaps.
Suction superheat temp reading cannot be higher than air on temp.

I think MAgoo has stated this in the past, possibly others as we'll.

Problem is solced completely only with replacing the orifice? are you sure there's no moisture in the system?

Yes Ranger was talking to the boss about this afterwards and he suggested I should have done that. I have been qualified for about a month its all so daunting still. Well I pulled the middle out of the old orifice and it was so dirty no chance it was letting anything through.

Superheat cannot have been the same on both Evaps... How were you checking your superheat