Walk in coldroom defrost problem

[Crypton]

I am getting a bit of grief with a coldroom in a restaurant we look after. About 3 months ago a probe went and the evap turned into a block of ice. Changed probe and defrost operated as normal. I got a call during the week went in and the control switch on the front of the panel was broken I bypassed the switch left running. A few days later they called me to say it was iced up again. Went in again defrosted evaporator. I put the unit on a manual defrost. All the heaters came on and with the help of a terbo torch I melted the ice. Checked the defrost settings. It comes on defrost every 4hours. Duration for 35 min. Defrost stop temp is 16C. Probes working. Unit pumping down. Solenoid ok. expansion valve is new. Everything seemed ok. Got a call again last night to say she had iced up again. I did notice last night the lads in the kitchen had set the fridge temp to -2. They are always complaining that its not cold enough in there even though fridge will pull down to 0c with no problem. Its a really busy kitchen and they are constantly opening the doors. The coldroom is designed for holding only and not pull down and they do put warm product in there the odd time. Has anyone any ideas why she keeps icing up? Thanks for your help

[cadwaladr]

can you lock the controller to stop it being set below 2 degrees c and set the diff to 3 degrees

[Crypton]

I can lock controller so they can't change temp. Do you think that's anything to do with defrost problem?

[mikeref]

Ah,am i missing something Crypton? Why are there defrost heaters in a coldroom? Anyway, sounds like high humidity and heatload+ long run cycle. Is the plant old and inefficient, clean coils etc... mike

[nike123]

Initiate manual defrost and see if it is terminated by evaporator temperature or time (not when it is blocked by ice, do that when is normally frosted).
Than take these measurements after cold-room reach 3-4°C.


Evap air/water in temp
Evap air/water out temp
Low side pressure or saturation temp
Suction line temp at evap outlet
Suction line temp at compressor inlet

Cond air/water in temp
Cond air/water out temp
High side pressure or saturation temp
Liquid line temp at receiver or condenser outlet
Liquid line temp at TXV inlet
The more information provided the more accurate the diagnosis.

[Magoo]

If a +2 'C chiller setup the LP switch to cycle off at desired temp, and back on after air defrost and clear coil. The staff can set controler at what ever they want, the LP switch will over ride controller. Then forget about the electric defrost. Knowing that chefs will leave door open all the time and kitchens are hot and steamy. you will be in control. Perhaps a door swithch and an annoying buzzer alarm will prompt them to close the door quicker.

[mikeref]

Magoo, i like the buzzer idea, have to put it out of sight so they can't wack it with a broom, then maybe off the same door switch cycle the evap fans...mike.

[coolhibby1875]

make sure you fitted the correct probe type, i got called to a zannotti room where a engineer had replaced the evap probe with what he thought was the right probe, except the original was ptc and he fitted ntc probe, so the probe reads out with the desired termination probe temperature therfore never goes onto defrost, worth checking out!!

[Crypton]

Thanks for your help lads. I am heading into restaurant tonight to do another job so I will have a good look at it. I have to say I like the buzzer idea. It would wreck their heads. I just presummed the probe was ok once there wasnt an E1 fault. I will check it out. The last time the evap was cleared was Sunday night so this evening I will have a good idea of how the coil is. I will post back up tomorrow if there has been any change. Thanks again for your help.

[barryjustin]

I had this similar problem. What brand of controller is the defrost? We had a late model dixell on ours, it was only about 6 months old, but every now and again it wouldnt switch to defrost properly. We changed the controller, and never had this problem again.