freezer coil icing up

[hutch]

Hi guys, ive got a problem with a walk in freezer . Evaperator freezing up every 3-4 days. Heater ok, refrigerant ok, controller new, exponsion valve new, its a small box 3 metre square. It starts icing up from the top right hand side, near the exponsion valve. Valve iced up as well. Note heater is at the bottom of coil on drip tray. Ice build up on back of coil so looking on coil when walk in freezer the front is clear of ice. Then it work its way to the front of coil. By this time temp drop from -18 -10 and below. controller set up as standard. Drip time defrost cycle ect. Any ideas would be appreciated thanks guys.

[licencetochill]

Hey Hutch,

Just a quick question,

Are you saying you don't have defrost elements in the coil itself? and just one in the drain tray?

You need at least one coil element, probably two.

[Justin_]

Presuming superheats are correct and gas charge ok, id have to say that the coil requires elements through the coil itself and not just on the drip tray (as licenced to chill suggested).

Ive never come across a freezer evap coil with no elements running through the coil...however I have seen medium temp applications with coils that u describe.

What are your defrost parameters?

[frostline]

New valve? Did you adjust the superheat? The txv should not ice up until the coil is quite iced up. If the valve body is icing up first the superheat is off. And I agree with the others, if the heat can't get to it the ice wont melt.....

[airtrackinc]

Check your refrigerant charge.

[hasfehal]

If the super-heat, defrost scenario, timing etc are all right, I would recommend you to check the material(meat, poultry etc) temperature and the frequency you open the door. We had a similar issue with a customer, when they didn't have time at the end of the day, they used to put the material-strawberry in this case- straight away inside the cold storage(-18 C ) without precooilng(or freezing) -IQF in this case-. If there is steam source -boiling water, or warm surrounding etc- opening the doors very often also causes humid gets in and the water condense on the coil then got frozen.
I hope you sort out the problem soon.
regards

[Magoo]

Coil being starved of liquid gives uneven ice build up and hard icing at TXV, check super heat of TXV.

[Dragonfall5]

I Went to a Similar Problem on a Walk-in Freezer Room, Found the Coil Temperature Probe 1/2 Inch above a Defrost heater element. Defrost would terminate almost immediately and Over 2 days the Coil would Resemble a Glacier.

[Mozambezi]

did anyone checked solenoid valve if it is passing by?