walk-in freezer evap icing up

[FEISTY]

Hello to all and hope business is good !! I have a situation that is driving me to drink....not that it's a bad thing ! I have been servicing a walk-in cooler that has entry door in large commercial kitchen. Curtains on door...condenser and evap coil sized correctly. All mechanicals replaced by me 2005. I am certain my problem is NOT mechanical related. I am convinced unit is at 150% capacity with overflow boxed product stacked on floor on plastic milk crates. I have 1 1/2-2" snow forming on both sides of evap coil. There is nothing forming in coil...only on surface of fins. Heaters all work. Defrost cycles 4hrs apart except for one 6 hour span during work time. Now here is my question. I believe problem is [1] overload of product, [2] lack of air circulation in box, and [3] humidity from cardboard boxes that hold 99% of stock. What would be the average humidity rating in a freezer set for 0-5 below far. Would a " tattletale " data recorder help to prove my point? If coil is 100% thawed and blown dry, coil will repeat freeze-up within 24 hrs. I feel I know the answer but would like opinions to share with higher-ups when I report on Weds. Thanks for any help and suggestions. When you have the worst problem...share it with the best source of answer !! Thanks again.

[mad fridgie]

Firstly you say ice is forming on both sides, do you mean air in to the evap coil and air out of the evap coil both have snow on them them.
Firstly have check the oriention of the air flow.
My first thought is that the evap fan blades are rotating in the wrong direction. (either fan mounted backward or the moter traving in the wrong direction.
Do you have an external trap on your drain.
Snow normally indicates air infiltration, but useally just on the air inlet side.
Is this system on a pump down, if so change it to non pump down. Just turn of the liquid solenoid valve. This will aid defrost. (better heat transfer)
Your drip tray element (check that this is not on all the time this could cause streaming in the evap box)

[FEISTY]

Thanks for feedback. Let me respond to each question. First this is a system that has been up and running for 5yrs. Fan motors were changed once due to electrical surge but that was 3yrs. ago. Blades are original direction with about 30% of curve outside the evap case cavity. The airflow is in the back..out the front with blades drawing over motors and exhausting into cooler. Next, drain pan is draining completely and has running style trap so we have no air draw back thru line. All heaters are powered off during freeze cycle except for drain line cable which is under 1/2" wall insultube. On defrost coil heaters and drain pan heater power up on demand. Next, yes it is wired as pumpdown solenoid operation. I have installed these systems this way 95% of the time as I was " factory taught " that it is beneficial to start up compressor at lower load to extend life of compressor. May be a sales pitch from mfg. but my rule is " if it ain't broke...don't re-invent the wheel ". Lastly this unit has run fault free and callback free since install. Except for mechanical failure of headmaster and evap motors, it has run like you hope for. It goes back to my " overstock of product causing poor air circulation and added humidity level causing the " snow build-up and not solid ice ". That's why I'm after some sort of " standard humidity level " acceptable in a freezer. The snow is corner to corner & same thickness on both entry and exit sides of coil. Tried to adj. fan blade location in and out on shaft but made no difference. Fall and winter into early spring season..not 1 callback. When ordering by cust. increased, so did problems. So there you go. If I can add any more info, just ask. I said add a second walk-in to store product and use existing box with entry door in kitchen as utility box. Less travel and split product load seems to be answer. But then I only have 18yrs experience. What the hell do I know???? Sorry. Just venting. Thanks.

[mad fridgie]

One presumes that you are loosing temperature, as the coils become blocked with snow.
You have stated that your problem becomes worse in spring through summer. This is times of high use.
Excess air infiltration.
Humidity in your room at -5F is going to be close to 100%, even if it was not, you are going to struggle to measure at these conditions.
You need to change your defrost method, Increase frequency, increased length, increase termination temp.
If this is how the client is using it then you have to give him choices, you have suggested another store.
Add an air curtain, maybe the plastic curtain is forced open, we all know that they are a pain in the arse.

[chilliwilly]

After reading your post its hard to think what it could be, like you say its worked alright for all these years but only recently its give problems. It would seem there is an increase in humidity. Is the overall enclosed space in good nick? no holes or panels missing.

I once had a problem with a coil icing up on a walkin, and it turned out to be that the door was wedged ajar by one of the kichen staff to try double it up as an air conditioner. I only found out because I went back the next day to pick something up I'd forgotten. And they said it was too warm in the back of the kitchen so they opened the door on the walkin too keep cooler.

I remedied the problem by fitting an extra prox type limit switch on the door that shut off the liquid sol valve and the evaporator fan when the door was opened. I also suggested to the owner with his instant approval, that I could put a timer on there as well that would operate a counter and a buzzer, if the door was open for longer than 5 minutes. That way he could monitor how long the door was opened for and how often. The frost problem dissapeared within a week.

[mikeref]

I replaced the refrigeration equipment in an older freezer room only to have similar problems, turned out the freezer room pannels were saturated.I did not get to see the old equipment running but it could not have possibly kept correct temperature. In your case, check if anyone has access to refrigeration controls,sometimes the owners are the problem.

[Peter_1]

Just a quick reply: if I see ice and especially solid ice, then I think on a defrost problem. If I see snow, fine snow, powder snow, then I think on air infiltration.

Where is the pressure safety valve for the freezer mounted if any?
Drain waterslot (siphon), water in it?
Door seals in good shape?
Is fan not waiting too long after a defrost where you then get a big pressure drop in the freezer once it starts running and throwing very cold air in the then warmer freezer?
Check once these 4 possible causes.

[Mild Bill]

I had a kitchen helper removing the potatos from the steamer, to the freezer, to speed up their cooling for the potato salad. I put a stop to that and aside from an occasional extended freezer loading party, the evaporator coil remained trouble free.

[FEISTY]

I wanted to thank everyone for their feedback and opinions. After several trips back to site, at different times , I tried to catch the unit failing. I finally found that the sealed back of the 3 wire fan-defrost termination switch was separating from the body when it heated up from voltage. Moisture got in and , between on and off, heating up and cooling down, it was making contact whenever it wanted. When cool the back closed up and could not be seen as a problem. As we all can agree, the worst thing there can be is an intermittent problem. Just break !!! Anyway...all is well. Changed the control and all is well. It didn't stay on defrost long enough to clear coil but worked to melt and refreeze often. Adding defrost cycles seemed to be the right thing to do but just made things worse. So...thanks again for all the help. That's how we build up that black book of ideas for the next time. Have a great and safe day !!!