Icing up Evaporator.

Hello,all,I need some help.
I have an Antonio Seveso evaporator installed by others in a Freezer Room.I have had ice ups on a couple of occaisions.The main one was a faulty drain heater,which I sorted out.
Now I get a small amount of ice build up on the bottom LHS of the Evapoator,which after some months, there is a build up ,just on a small part on this side top to bottom.All heaters are working.Defrost is controlled by Evaporator sensor located at the centre of Evap.I have also noticed on the Expansion valve side of the Evap,the ice build up on the distributor pipes is excessive.This área after several months is unusually covered in thick ice.
I have altered the defrost termination temperature,and now get some ice droplets on the ceiling above the evap.I think it is a manufacturing fault,the manufacturer has since closed down.Any ideas would be very welcome. Jo.

Have you got enough gas in the system

You need service engineer attention to that problem. In order to give you some meaningful information, we need some measurements done and recorded.

How many evaporator fans do you have? Are you sure the left hand motor is working? Might seem a silly question but sometimes they can appear to be working but are actually just being pulled round by the others. Have you measured the superheat across evaporator? What refrigerant is the system using? Is there any frost at the compressor? Are your defrost heaters pushed right through the evaporator coil? Sometimes they can shift left or right, out to one side leaving a small area top to bottom, as you have described, with no heaters. More info required.

Quote:

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Originally Posted by NewmanRef

How many evaporator fans do you have? Are you sure the left hand motor is working? Might seem a silly question but sometimes they can appear to be working but are actually just being pulled round by the others. Have you measured the superheat across evaporator? What refrigerant is the system using? Is there any frost at the compressor? Are your defrost heaters pushed right through the evaporator coil? Sometimes they can shift left or right, out to one side leaving a small area top to bottom, as you have described, with no heaters. More info required.

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this, plus check if all the panels are in place and in order so that the air goes through the evaporator itself and not finding it's way through places where it shouldn't go :)

4 Evap fans.Have checked each one all working.Superheat check for R404a-5.Heaters threaded through evap left to right.One set on bottom side of evap on drip pan.3 set of heaters original.Thanks for reply back.

I am a service engineer.Just a little stuck.

Sight glass is clear and have the correct SH.This is strange.The last time I cleaned the coil,I left it with no ice.Put it back into operation and had the staff keep an eye on ice build up.Went back about a month later and a small amount of ice was starting to collect on the same spot from back to front.Went back 2 weeks later and this ice had started collecting up.3 months later there is an accumulation of approx 20cm top to bottom on the left hand side as before.The área where the connections and coil return tubes is full of ice also??What do you think?Thanks for your reply.

How long is the defrost cycle?
is there anything controlling the fan start?

Sounds like there is moisture entering the room from somewhere, or moisture in the air.
is there a N connection on the drain pipe, if not it could be drawing moist air in through the drain pipe.

Another thing could be if the fans start right after a defrost it will throw droplets or moisture out into the air, the fans should be set to start once the temperature of the coil sensor is -5 degrees to ensure that any moisture left on the coil is frozen to the coils instead of being thrown out into the room.

is this an evaporator with a simple thermostatic expansion valve or is it another kind of valve?

Thanks,yes.

Defrost cycle controlled by Dixell microprocessor.Fans conrolled by evap sensor.Drain pipe goes out to back of F/room with no access.Sorry for my ignorance,what is a N connection?
Fans controlled to start at-2ºC.Uses TXV.Regards.

I am a service engineer.

There are four fans.That was my first thought.Connected each fan individually.
SH of 6
R404ª.Compressor clean,just some usual moisture.
Heaters correctly installed.I changed the drip pan heater as it was shorted,with same KW.
Was there this week and the same has happened.Coil is clear,except +- 300mm on LHS top to bottom with ice.
Totally confused.

Not familiar with these coolers but one thing to check is the direction the fan is blowing. A lot of these fans have a capacitor which if faulty will cause fan to run backways.Also if 3 phase could be wired in reverse.Stick a plastic bag up to front of fan guard and you will know.

hi
you did not mention how many defrost in 24 hour and at what temperature defrost will stop defrost duration location of evaporator sensor I suggest to monitor the defrost you can start by manually defrost and see what happening if all evaporator is free from ice if not you can raise defrost termination to get the required result and the defrost cycle every 4-5 hours &good luck

Quote:

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Originally Posted by sacoolman

Defrost cycle controlled by Dixell microprocessor.Fans conrolled by evap sensor.Drain pipe goes out to back of F/room with no access.Sorry for my ignorance,what is a N connection?
Fans controlled to start at-2ºC.Uses TXV.Regards.

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Don't know the english word for it, so called it an N connection :)

meant a trap like this:
Attachment 11655

a trap like this should be on the drain pipe outside the coldroom, don't work too often on systems like this, but something I see often is that there is no trap and the drainpipe just goes through the wall and into a drain.
this causes moist air to be sucked through the drain pipe and straight up into the evaporator.

another big hit is not having heating cable in or around the drainpipe itself, causing it to freeze up and leaving the water from the defrost to stay in the drip pan where it quickly goes back up into the evap :)