Urgent help on cake counter

[MattR]

Hi guys

I'm having some trouble with a cake counter fridge in a bakery shop, it's running on r134a and a internally equalised TEV with a no. 1 oraffice.
The evap is a tubed bed in which the cakes sit.
This fridge was showing on the suction on arrival 10psi and wasn't cooling properly, I've tried changing the oraffice incase that was blocked, then the whole TEV, to no avail!
I've then tried changing the comp but I'm still getting 10psi suction and about 170psi... Ish on the liquid!! Any suggestions?

[The Viking]

Subcooling?
Superheat?
Temperature drop along the pipework?

All these questions...



.

[Luke.G]

SH?
SC?
All mechanical parts ok such as evap fans & condenser fans?
clean heat exchangers?
any other components on the system such as a LL Drier or LL SV?
nothing to restrict flow anywhere.......
Your SH & SC values should tell you really.....


Thanks,
Luke

[install monkey]

dont eat the cake!!

Hi guys

I'm having some trouble with a cake counter fridge in a bakery shop, it's running on r134a and a internally equalised TEV with a no. 1 oraffice.
The evap is a tubed bed in which the cakes sit.
This fridge was showing on the suction on arrival 10psi and wasn't cooling properly, I've tried changing the oraffice incase that was blocked, then the whole TEV, to no avail!
I've then tried changing the comp but I'm still getting 10psi suction and about 170psi... Ish on the liquid!! Any suggestions?

[frank]

Hi guys

I'm having some trouble with a cake counter fridge in a bakery shop, it's running on r134a and a internally equalised TEV with a no. 1 oraffice.
The evap is a tubed bed in which the cakes sit.
This fridge was showing on the suction on arrival 10psi and wasn't cooling properly, I've tried changing the oraffice incase that was blocked, then the whole TEV, to no avail!
I've then tried changing the comp but I'm still getting 10psi suction and about 170psi... Ish on the liquid!! Any suggestions?

Back to basics....

How do you determine that it isn't cooling properly? Is it meeting set point temperature or are you just using the suction pressure as a guide?

Why did you change the TEV just because the suction pressure was at 10psig?

R134a at 10psig gives a saturated suction temperature of -14.1C. What is the suction pipe tempurature? What is the set point?

Is the compressor hot to touch? Is it drawing current near to the plate rating?

Without more information, it will be difficult to give an accurate diagnosis...just best guess suggestions.

[MattR]

@the Viking and @luke... Cheers for your replies lads, I'll be honest I've not tested superheat values since college and am quite unsure how to do it, I know how to physically do it, by adjusting the screw kn the TEV but it's just the checking part??

[The Viking]

OK,
If you give us the head pressure and the liquid line temperature as it exits the condensor I will give you the sub cooling.
Take a further liquid line temperature before (~4") the TEV just to check for temperature drop.

Then give us the suction pressure and teh temperature of the suction line where it exit the evaporator/the TEV bulb is fitted and I will give you the superheat.

Compressor discharge temperature will also help

All readings to be taken after a minimum of 10 minutes running, the more accurate the readings the better the diagnostic will be.



.

[MattR]

@frank
Hi mate, I was told by the previous engineer and the shop owner that it wasnt cooling properly, however it does meet the set point of 4'c. I changed the TEV as I thought it may have been blocked as when I changed the oraffice there was black powder in the pipe work and valve. The compressor was just warm to touch just like you would expect to be fair.
Cheers for your help guys
Matt

[The Viking]

That "black powder" is most likely soot from when someone has carried out brazing without at the same time flushing the system with OFN.

That is a real killer...

If it reach setpoint then it is cooling.

The question is how far you are taking it.
With proper readings and adjustments you will get a more energy efficient system.
But if the soot is left in the system then energy efficiency will be the least of your troubles.



.

[MattR]

@the Viking, I am unfortunately not at the cabinet until the morning, however the discharge pressure was around 170 psi and hot coming off the comp but was strangely relatively cool at the exit of the condenser, not Luke warm like you'd expect? This concerned me first off, the sight glass read full with no or very little flashing sort of as you'd expect but I'm still having the trouble with 10psi suction, no matter what I do I can't raise it? Their is no frosting coming off the evap exit and where the bulb is, but is still cold obviously. I'm sorry I can't get accurate reading until the morning but I'm losing my mind with it now

[install monkey]

check for a temp drop accross the drier, ensure the tev bulb is mounted correctly,and insulated. then degas and comfirm the charge is correct.

[MattR]

There is no temp drop across the drier as I checked that and changed it just incase, it is a bespoke counter and unfortunately has no data plates stating refrigerant charge or electrical info at all

[mad fridgie]

was there frost coming out of the evap?
If yes, then it is doing what it can, if no increase the orifice size.

[MattR]

Thanks for the reply, if I increase the oraffice though surely it will make my 10psi problem worse? I don't think there is frost on the exit though to be fair. Would you say make it a size 2 instead of 1 then??

[mad fridgie]

Thanks for the reply, if I increase the oraffice though surely it will make my 10psi problem worse? I don't think there is frost on the exit though to be fair. Would you say make it a size 2 instead of 1 then??

Next size up!
what do you mean will make it worse. If you are staving the evap, the bigger orifice will increase the pressure.

[mikeref]

MattR, something to think about.
Maybe the compressor was replaced some time prior to your visit and that compressor was incorrectly sized. As in too big. Run your hand down the side of the condenser and see if there is a gradual reduction of temperature, or a quick change from hot to cold.
What is the cabinet measurements?
Are you sure it is supposed to run on R134a? Some small cases here run R404a.
Put on your detective hat and ask the owner about any work previously carried out on this cabinet.

[MattR]

Hmm, I can never really tell about previous work as I'm going to these jobs after a previous engineer that knew very little and has often made silly mistakes, the shop owner was always kept in the dark as to what work took place!
I think the comp is the right size as the temp down the condenser is gradual but it's cool at the bottom not warm?? It also runs on 134a in quite sure of that as 99% of these cabinets i work on do, It reaches it's set point fine it's just the 10psi suction? I may try sticking a size 2 oraffice in it to see if this works as that makes sense now coming to think about it
Thanks for all your advice, your getting me out of what was quite a hard place

[frank]

With the condenser being rather cool at the bottom and the liquid line also cool you need to check your sub cool measurements.

[The Viking]

MattR,

You have to start sorting between the answers you get.
Until you properly assessed the situation (by measuring the running conditions properly, incl SC and SH) mindlessly throwing new parts at it or replacing orifices will do neither you nor the cabinet any good.

Why would you replace the orifice unless you first know for sure that the existing one isn't good enough?
Checking the running conditions should be a 15min job, reclaiming/opening/pressure testing/vacuuming/recommissioning the system to change the orifice will take you much longer...



.

[MattR]

MattR,

You have to start sorting between the answers you get.
Until you properly assessed the situation (by measuring the running conditions properly, incl SC and SH) mindlessly throwing new parts at it or replacing orifices will do neither you nor the cabinet any good.

Why would you replace the orifice unless you first know for sure that the existing one isn't good enough?
Checking the running conditions should be a 15min job, reclaiming/opening/pressure testing/vacuuming/recommissioning the system to change the orifice will take you much longer...



.

Okay I have been back today and have run the system looked at the superheats which all look as if to be fine! ive looked closer into the valve, orrafice size compared to the comp size all results are looking good. I have spoke to a couple of engineers now and talked about these bespoke fridges, i cant see it phisically but i think that soot from past brazing work etc has blocked a distributor port thats hidden between the top bed and the cabinet base. looking at the pattern of frost on the bed it looks like the refrigerant is taking a easy route through the top of the bed and not so much at the bottom, i know similar results would be expected on a fully functional cabinet but this can be the only explanation for the pressure drop.

[monkey spanners]

Blocked orifice i found, this system had a burnout and compressor replacement a few months before. Don't think you would get enough oxide from brazing to block these up, it takes a motor melt down or some incompatability of refrigerant, oil etc to make a this much cr@p imho.

Shows it about 4minutes 10 seconds in,

http://www.youtube.com/watch?v=WkLfIGCBZ2M

This one also,

http://www.youtube.com/watch?v=Lo3YD0Fy5yM


Jon

[al]

Your initial question states fixed orifice, is it a standard TEV with a bulb off it or an older AEV? Have you a receiver on the unit, also could you stop mucking about and give the temperatures requested, (i say this in a nice tone of voice), i've seen many bespoke cabinets with undersized condensing units fitted (counterline are feckers for this), so step one: temperatures; step two TEV or AEV (if unsure post a pic of valve and evaporator)

al

[1torr]

Hi, if its reaching temp of 4 deg c, measure the superheat, if its around 5-6k and you havnt got an excessive discharge superheat value. Plus you say it runs with a clear sight glass. Whats to worry about?

[Royal241]

i don't know about you guys, but I'm confused. A cap tube with an expansion valve and a sight glass? You lost me there dude ...

[MattR]

Ahhh not a cap tube a small peice of pipe branching off a distributer that may be buried in the cabinet somewhere mate.