icing up on evaporative coil!!!

[phanhuy183000]

hi all,
i'm working on freezer with two evap coils, low temp -16.
defrost is working ( 5times a day, 30mins), heater elements r working
Superheat 6,5k at the left evap which was icing up after two days manual defrost
low pressure is 22psi ,no buble at sight glass
the right evap coil is ok, fans are ok
thanks for any advice

[Rob White]

hi all,
i'm working on freezer with two evap coils, low temp -16.
defrost is working ( 5times a day, 30mins), heater elements r working
Superheat 6,5k at the left evap which was icing up after two days manual defrost
low pressure is 22psi ,no buble at sight glass
the right evap coil is ok, fans are ok
thanks for any advice

If both are the same and they are both working correctly
then I would look to outside influences.

So is the left evap near the door or air vent?

Regards

Rob

.

[phanhuy183000]

Thanks for your advices ,rob.
They are both same horizontal position, proper seal.
The piperun is 10 metres, and SH at evap 6,5k, but 18-20k at compressor.
Im wondering which sh that we are looking for
The right evap is ok but left evap was iced after few days
Thanks

[Rob White]

.

Do the evaps have schrader valves fitted near where the
TEV bulb is so you can read them individually?

Do the evaps have solenoid valves (mag valves) fitted?

Don't worry about the superheat at the comp, it will be higher
than at the evap. The important one is superheat at each evap.

Go back to basics, firstly

Check evap fan rotation (if cap start single phase, they can run in reverse)
Measure the air temperature onto each evap and the air temp off
Is one evap closer to the comp than the other?
Is there one mag valve for each liquid supply to each evap?
Is the ice snowy or solid clear ice?
Does the evap ice up evenly or is it just to one side, bottom or top?
Are there door switches fitted to stop fan when door open?
Is one evap nearer to the door?


Regards

Rob

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[joe-ice]

Also verify the defrost termination probes are reading correctly.If probe is faulty could be reading high temperature and defrost will not initiate

[richelli]

Is the ice clearing on defrost? If not and each Evap has its own solenoid valve, is the valve on that Evap passing and not allowing a correct defrost.

Is the Evap reaching defrost termination temp? If not does it need more time or is there a faulty probe if its working off a probe or defrost stat if its done that way.

[lawrence1]

Is the ice clearing on defrost? If not and each Evap has its own solenoid valve, is the valve on that Evap passing and not allowing a correct defrost.

Is the Evap reaching defrost termination temp? If not does it need more time or is there a faulty probe if its working off a probe or defrost stat if its done that way.

5 defrosts per day @ 30mins seems excessive,,,is it a coldroom /glass door freezer/open island case?
i suspect the too frequent defrosts are steaming the refrigerated area causing the frost.

[Kherson]

My guess is that your right coil isn't getting any liquid in the first place. Shut-down the left coil for a day, if you can and see what happens...
Kherson

[phanhuy183000]

988798889889
I checked the unit last week
Both evaps got the right rotation fans
no door switch, no magnetic valves on evaps
Left evap : air in (-4.5) air out (-5) room temp (-4),LP 20psi coil clear ok ,
right evap: air in (-4.5) air out (-6) room temp (-4),LP 20psi icy snowy on top
left evap (10metres) and right evap(7 metres) to compressor .

I found only one coil sensor for the 2 evaps and the sensor was installed at middle of right coil . When I opened the doors next to the right evap coil then the fan was stopped and comp run still.
the fan,comp were running ok when the left doors opened
I relocated the coil sensor from middle to top right coil then the fan,comp were running ok
I thought something wrong with the coil sensor. Should I relocate the sensor somewhere or install another one for the right evap? is that the reason to make the right coil icing up?
Thanks for your helps and advices

[install monkey]

are the doors sealing correctly on the right hand door?

[phanhuy183000]

are the doors sealing correctly on the right hand door?

Yes,it's good condition as per pictures

[install monkey]

you mentioned when you opened the right hand door the right evap fan stopped, either pipe sensor or fan failing, is there a overheat klixon in the fan windings, or a bad connection?? swap the fans over to prove this

[chilliwilly]

When you say the coil sensor are you refering to the XV phial/thermistor?

I have a similiar problem with an evaporator in a walkin at a butchers shop. The original complaint was the walkin wasn't pulling down, I suspected a leak but unable to find one after checking. Suspected that it was under charged as it turned out that the previous occupier had had a replacement air handler unit a few months before, but it looks too big for the walkin and maybe under charged. Started to top off and found the pot/compressor sweating almost immediately and started grunting an evap coil had iced up.

I need to go back and check the XV phial is actually secured to the end of the coil and not throwing the superheat out, and whether or not its overcharged. But they need to move the meat out as no access to air handler.

Another time I had a similar problem, was the controller defrost o/p was shorted and bringing on the
the heater all the time causing the XV to flood the evaporator. As there were three seperate heaters and only one of them working which was the one closest to the phial.

I've always said that hot gas defrost is superior to electric because of this potential problem.

[richelli]

Sorry if I miss understand your post but you say when you open the right hand door the fans stop but the left hand side they don't? If this is the case has someone linked the door switch out on the left hand side so the fans don't stop?

I would make each Evap have its own defrost termination. You could get more ice on one Evap if the doors in front of that one are opened more during the day, so maybe it needs a longer defrost.

In your first post you say it's the left hand Evap icing up but then you say it's the right in a later post?

As Kherson wrote above, is the right hand Evap starved of refrigerant causing the left hand Evap do all the work? Have you checked to see that the expansion valve filter isn't blocked with crap.

What gas is this system running on?

[phanhuy183000]

I did mistake! The right hand evap iced up. The left was ok
Only one dixell coil probe/ sensor at middle right hand coil evap.
The left coil doesn't have probe.
After I relocated the probe from bottom to top icing right hand coil. The fan running continuously even the door opened.
Fans are ok
The unit is on r404a

[Rob White]

.

Has it always done it? or is this something recent?

If it has only just started or only just been noticed then
What has changed?

Has the unit had any work done to it? you

You also say air on and off is -4.5 on and -5 or -6 off?
In your first post you say the thing is at -16?

If it is -4 & -6 that seems wrong for a freezer. I would have thought
temperature difference (TD) would be nearer 10 degs not 2 degs.

Is it a fresh meat case and temp in case at 0 deg C?

2 degs TD over the evap for fresh meat is normal.

Rob

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[Rob White]

.

What is the defrost method

Is off cycle or does it have heaters?

It will make a big difference.

Rob

.

[phanhuy183000]

The freezer temperature can pull down -16 ,the details i posted when room temp -4, i fixed the gas leak and charged right amount of gas (Sh, sight glass checked ok).the coil evap defrost by 2 heater elements.

[Rob White]

.

Did you remove the charge and weigh in new refrigerant
Or did you bring the levels up to clear the sight glass?

A few things are wrong here I think :eek:

You need to measure the air onto the evap and the air off
when the case is down to temperature.

2 deg C difference over that coil does not seem correct, it
should be nearer 10 degs.

Under what circumstances was it at -6?

When the doors are opened does the temp shoot up?

I think there are a lot more things with this system than you think.

First it has had a leak
You repaired leak
You add refrigerant
The case run down to -16
The case is at -6
One evap frosts over
One evap does not frost over
What's the stock rotation like? are the doors always open?
Do customers stand with the doors open while looking at the stock?
Is there a fan blower, heater, AC near to the iced up one that could influence it?
Is the right hand one used more than the left?
Are ther any dividers between the two cases?

You have got a series of issues all related and effecting
the operation of the system and then there are small niggly
things you don't mention, like the system being short of gas
and you adding some more.

Rob

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[Rob White]

The freezer temperature can pull down -16 ,the details i posted when room temp -4, i fixed the gas leak and charged right amount of gas (Sh, sight glass checked ok).the coil evap defrost by 2 heater elements.

Did you top up the system or did you remove the whole charge and start with new refrigerant?
Did you replace the dryer?
Is the dryer before or after the sight glass?
Is there a temperature difference over the dryer?

Rob

.

[richelli]

Rob is correct in that you aren't giving a clear story here so we are all just guessing! Rob is giving you good advice but he needs good information.

[install monkey]

are all the defrost heaters ok, clip the current on all elements

[phanhuy183000]

I took over this job from s.o who did not install the freezer properly. The unit has had gas leak and right evap frost over .i fixed the leak and top up refrigerant without changing liquid filter drier. The unit temperature can pull down -16 .
No divider between two cases, the doors close all the time, only open when the stock taken
Thanks for your information all

[Rob White]

.

There is obviously a difference between the two coils.

I would look to liquid starvation across the dryer.
I would look at whether the Expansion valve filters are clean.
I would look at the blend of 404a, if you have had a leak and "topped up"
there is a small possibility of the refrigerant being wrong.

Regards

Rob

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[Tycho]

1. Are you sure the heating elements are working?
2. have you checked if the solenoid is leaking internally during defrost?
3. have you been there and watched a defrost to see if the coil defrosts properly?
4. Does the water drain properly from the drain pan?
5. is there a water trap on the drain pipe from the evaporator, cause if not it will pull moisture through the pipe
6. are all the covers in place so that air passes properly through the coil?

[Tycho]

and what did you find out?

[fixesanything]

I have a related problem, System R404a no defrost as its a cool room minimum 4 c, On a ship
I am presently getting the door seals replaced as they are less than perfect, Fans are running and stop when door switch is active direction ok

The previous engineer topped up the gas and when i asked the junior engineer who helped him how they did this it seems they may have just used the bottle up right.

I have checked and there does not seem to be a tube going down to the bottom of the bottle so i am assuming the gas blend has been screwed up ie not liquid filled,

Apart from excessive frost the cool box seems ok. Though compressor does seem to run a long time which may affect the frost as in this case its the fans running when the compressor is off that does the defrost.

What would be the problems associated with a pure gas top up on a system that should have a gas blend ie 404A ?

[jamieson91]

Purple of basics mate I get problems like this from time to time I'm in Australia Queensland I look after woolworths stores,bws and pubs owned by woolies .. Most common occurrences are
1. TXV will appear fine,spring pressure fine, bulb pressure etc ll ok but when a system has run short for a period of time it wears out the needle and the txv stats to hunt irregularly and ices up in a matter of days ... Very tricky to pick just have to go with the gut sometimes as its not the typical loss of bulb charge or blockage.

2. In-efficient compressor (make sure you watch to see if discharge valve is sealing ...)

3. Over condensing in the winter months ( do you have fan speed controllers )

4. Dirty condenser ... Might look clean but I always give mine a hose and de grease and am always shocked to see what comes out ...

All of the above usually result. In longer run time periods causing ice ups
I always get the "maybe they left the door open" from fellow techs and just wat for the call babacks another thing I find from time to time is when the defrost is time based or temperature terminated that the defrost termination temperatures are too low as the defrost probe is too close to the elements... I found that a problem from factory on skope blast coolers and under bench freezers.
Just out of curiosity set the defrost then isolate the power and startup the control circuit again ... Come back 15 minutes before it is scheduled to go into defrost and make sure it is coming in on its own...
I also have problems with busy freezer rooms with not heat exchange room or door curtains in summer ... Huge humidity up my way just sucks straight on to the coils ..

last but not least ... Have you checked your explosion port ?