Walk in fridge problem, any advice??

[Northdude]

Hi guys, i have been having a lot of problems with a walk in fridge over the past few weeks. Its a small pump down system.On my first visit the system was off on LP but it had not lost its gas, managed to trace it down to the gas not getting through the expansion valve causin it to pump down so i replaced the expansion valve, vac"d and charged it. System running fine for a week then the same thing happens again. I suspect moisture in the system causing the valve to choke up so i took expansion valve off, put nitrogen through all the pipes, replaced exp valve and orophus, replaced dryer,carried out a triple vac and then long vac after that, charged system up and everything working correctly for 10 days until yesterday i got called back and it was the same fault again, the gas isnt getting through the exp valve. The solenoid valve on it is fine. The external equalising line is a bit kinked off the exp valve would this have an affect? i havent had a lot to do with exp valves in the past only replaced a few, but this has me stumped, any ideas?? Thanks in advance.

[DTLarca]

Is the condenser located outdoors? If so, what sort of head pressure control is employed?

[Quality]

Agree with the above it sounds like it suffering from them cold

[Northdude]

yes the condensor is aboove the coldroom on a small flat roof outside, what do you mean by head pressure controls? The coldroom is only 2m x 2m so the condensing unit is really small which basically consists of a dryer, hp lp switch and solenoid there are no other controls on it, cond fan is fixed speed.
This problem did start as soon as the bad weather arrived with ambient temps between 0 - 2 degrees celcius if that could be a factor.

[Quality]

Due too the very low ambient temp the condensing unit is not able to produce enough head pressure / temp which prevents proper condensing

Head pressure control means exactly that controlling the discharge pressure by reducing then condenser fan speed to achieve a suitable condensing temp

[jpsmith1cm]

Where is the pressure control set?

I normally set them to cut in about 5 degrees below the lowest expected ambient temp. Around here, that's about -25F, so convert to pressure and set the control.

The overriding factor is that I won't set most controls to cut out in a vacuum.

Does the unit have enough charge?

[chemi-cool]

By head pressure control, he means that you should install an extra auto reset high pressure control that will start the condenser fan on a pressure that is high enough to push the refrigerant through the TEV.

You did not state the refrigerant in the system so I can not tell you how to set it up.

[Northdude]

I see what you mean, the system is on R404A refrigerant.

[chemi-cool]

OK. Than set to start the fan at 280 psi and stop it at 250 psi, this will let run much better.

[Northdude]

Hi JP, the pressure control if i remember correctly is set to cut off at around 2 psi and cut in at around 20 psi. The refrigerant charge on it is fine, its around 45 psi (suction) when running. I need to call back tomorrow morning but dont have a lot of time, if i partially blocked the condensor coil would get it going untill i call back through the week?

[Northdude]

Ok, thanks Chemi

[DTLarca]

Hi JP, the pressure control if i remember correctly is set to cut off at around 2 psi and cut in at around 20 psi. The refrigerant charge on it is fine, its around 45 psi (suction) when running. I need to call back tomorrow morning but dont have a lot of time, if i partially blocked the condensor coil would get it going untill i call back through the week?

Block the top 2/3rds for the next month.

[Northdude]

Ok, thanks DT :D

[jpsmith1cm]

Hi JP, the pressure control if i remember correctly is set to cut off at around 2 psi and cut in at around 20 psi. The refrigerant charge on it is fine, its around 45 psi (suction) when running. I need to call back tomorrow morning but dont have a lot of time, if i partially blocked the condensor coil would get it going untill i call back through the week?


Cut in is a little high IMO.

I don't know your ambients, but I'd set the cut in on a 404a system at about 5 or 6#.

[mbreward]

Most TX valves require 10 bar differential accross them to operate correctly, so if you install a pressurestat to stop the condenser fan at 10 bar above suction pressure & start the fan at about 4 bar higher this should prevent over-condensing
The high-tec solution is a condensor fan speed controller but that may be ott for a small system

[Robert Hilton]

Slightly off topic Northdude but this is my advice for a walk in fridge
http://www.youtube.com/watch?v=yIutgtzwhAc

Cheers,

Rob

[Gary]

Unkink the equalizer line.

[charlie patt]

had the same probs lately and found oil blockage due to tev installed on its side i turned tev 45degrees and never missed a beat since

[Northdude]

This job has came back to haunt me, i partially blocked the condensor before christmas (would have fitted a fsc but it is a really small system), i got called out to it on boxing day and when i arrived it has sorted itself out and was down to 4 degrees then yesterday i got called back again. Found system off on LP with suction at 5 psi, there is a suction port in the coldroom off the evaporator, pressure was at 8psi then i heard the gas spurge through the exp valve and pressure rose to 15psi then stopped for a few minutes then heard the gas again through the valve and suction rose to 25 psi then compressor cut in and pressure shot down to 5psi and went off on LP. when i took my line off the suction port there was dirty oily water on the end of the suction valve. It would seem the TEV is blocked, i replaced the TEV about 6 weeks ago and the orophus and triple vaccd the system. The condensor is located directly above the coldroom on a flat roof, what do you guys make of this? The TEV is installed in the right position.

[charlie patt]

Can you give a better discription of fluid ? I pressume due to outdoor condensor it does not have a revap coil? If you warmed up tev did it run ok also being a small room is it a internall tev please advise

[Northdude]

Hi charlie, the fluid was more like mirky water, i have not tried to warm up tev, tev is external, there is no revap coil. thanks

[DTLarca]

Here is an article that might be related...

[Northdude]

Thanks DT, i was thinking it could be oil, when the compressor does run and it starts to pump down the tev starts to ice up really bad after the orofice so its not completley choked, im going back to the job in the morning, im not certain on the cause so dont fancy replacing everything again.

[monkey spanners]

Sounds like there is quite a bit of water in the system.

The favourite way for it to get in is a leak on the tev out let, especially when the system is on pumpdown and the lp switch cuts out below 0psi.

I would remove the refrigerant, and look for leaks with ofn. If the system is really wet then i would put some fresh oil in the comp, fit some oversized driers, and some fresh refrigerant.

I have had a few systems like this and rather than replace the tev you can warm them, not too hot, just enough so that you can still touch them comfortably. This will get things moving again, maybe for a few minutes, or days depending on how bad things are.

It might be worth blowing through various bits of the system with ofn to get ant free water out while you have it in bits.

Jon :)

[Northdude]

Yes Jon, this is what i suspected the first time i got called out, i did blast OFN down all the lines etc after that it went for about a month before i got called back so there must be a leak somewhere. Thanks for the advice!!

[mad fridgie]

You need to find your cause first, I suspect that you have a leak on the low side and your cut off setting is likely to be less than 0 PSI (calibrate your gauges), you say you have a kinked equalizer line, good place to start (there may be a hair line crack) when checking gentley add a bit stress back and forword to the pipework (the leak may only appear due the expansion and contraction)
The oil is know badly contaminated, remove if possible, if not possible, heat compressor to quite warm temp 60 -100C whilst completeing deep vac.

[charlie patt]

mf has got it nailed just fit a torr gauge and a nice solid core drier

[cadwaladr]

hope you got it sorted,i always try to use sporlan/alco driers if i was you put a drier in the suction line too,thats as long as it still has no leaks.