Frosting of evaporator coil

[Cofreth]

Hi,
Any idea what is the usual cause for evaporator coil blocked with ice rendering the system not cold?
What is the recommended defrost timing and max no. of times within 24 hour.
Average ambient temperature in the supermarket around 23 to 25 degree C and RH80%.

Tks,

[chemi-cool]

Hi Cofreth,

The main reason for frost is high humidity inside the case.

Is there a fan employed for air circulation or is it static one?

The defrost, is it hot gas or electric?

The recommended defrost times/intervals, depends on humidity, No of opening times and experience.

What is the desired temp in the case?
An iced coil will not cool.

Chemi

[Cofreth]

Hi Cofreth,

The main reason for frost is high humidity inside the case.

Is there a fan employed for air circulation or is it static one?

The defrost, is it hot gas or electric?

The recommended defrost times/intervals, depends on humidity, No of opening times and experience.

What is the desired temp in the case?
An iced coil will not cool.

Chemi

Is there a fan employed for air circulation or is it static one?
There are 4 fans circulating air within the multi-deck freezer.

The defrost, is it hot gas or electric?
Electric Heater.

The recommended defrost times/intervals, depends on humidity, No of opening times and experience.
It's a multi-deck low temp showcase with desire temp of -20 degree C.

[Bones]

i feel it would need defrost at least 3 to 4 times a day (24hr period)...

how is the defrost situated at the moment how many times for how long?... if you dont allow enough defrosts or for long enough time you'll get ice buildup fast...

with a supermarket too (i'm not a supermarket man persay) but heavy access to cabinets or door not closed properly for long extended periods could cause large ice build up

[chillin out]

with a supermarket too (i'm not a supermarket man persay) but heavy access to cabinets or door not closed properly for long extended periods could cause large ice build up

This is true, but, the evap fins should always clear itself. There maybe lots of frost on the walls and ceiling but the defost system should clear any frost/ice from the evap.

I beleive this is an excuse for an engineer not being able to repair a fault.

One of the sites I attend has the door nearly hanging off (waiting for the go-ahead to get replaced) and the coil is clear. Granted the rest of the room is like a snowdrift.

[Bones]

This is true, but, the evap fins should always clear itself. There maybe lots of frost on the walls and ceiling but the defost system should clear any frost/ice from the evap.

I beleive this is an excuse for an engineer not being able to repair a fault.

One of the sites I attend has the door nearly hanging off (waiting for the go-ahead to get replaced) and the coil is clear. Granted the rest of the room is like a snowdrift.

It always helps if the system is one which you maintain through a service contract on a regular or semi-regular basis, but 98% of the time people only call you when there is a problem they cannot fix themselves, and by this i mean they'll try to fix it themselves first before ringing.

Also it often helps if they answer simple questions asked about there fridge/freezer to know what to undo before starting to look for the real problem...

At the humidity implied it wouldnt take long for the coil to start icing especically in a freezer coil, this would only be amplified by not enough defrosts to clear coil, or if the defrosts are timed rather then DTT controled not timed long enough to allow for all the ice to be wiped off the coil.

Could also be a dead or half dead element, was the element tested?

Also lets face it, being a supermarket, people shopping dont pay the electricity bills and often open the doors for exessive times whilst looking for what they want rather then waiting until they know what they do want, It all helps to amplify the problem.

[Dns]

Hi,

Seems to me that you are talking about Air-conditioning system?
The reasons may by as follows:-
1. The Evaporator fan might not be working.
2. Evaporator coils dirty.
3. Not enough refrigerant.

[Cofreth]

Hi Dns,
Are you also doing refrigeration equipment here?

[Derek]

And again make sure the drain line is clear and has a P trap or all that nice warm wet air just rushes back in....

[Manoj Menon]

Hi..

Do the system having automatic defrost termination?. If so you can fix 30 mts X 4 times/24Hrs. Even though you have to monitor the frost thickness in 2-3 days. If 30 mts is not suficient then you have to increase 5 more mts. you have to continue till you gets correct time. The amount of frosting will be defferent in all defrosting cycle. for egsample frosting at mid night will be less. early morning will be hardly anything. If defrost termination ( when the coil temperature reaches +ve, the the compressor should stsrt automatically) is not provided it is highly defficult to adjust defrost. More duration will lead high heating and less duration will lead high frosting.

[Cofreth]

I have 6 times a day every time last for 20 min and during defrosting, the solenoid valve is shut, but the evaporator fans are still running. It takes a long time to pull down to require temperature after defrost, sometimes triggering the high temperature alarm in the middle of the night, whoever on duty will need to attend to it.

[Konrad Knoesen]

Hi Cofreth
Sounds like you are using an electronic controller here.Being a freezer you dealing with,the controller should be equiped with two sensor probes,one for temperature and one for defrost.The defrost sensor could be faulty,giving false readings and preventing a defrost cycle from happening.You should re-configure the parameters,especially the alarm delay.Could be the controller going faulty as well.Hope the info helps....

[Abe]

I have 6 times a day every time last for 20 min and during defrosting, the solenoid valve is shut, but the evaporator fans are still running. It takes a long time to pull down to require temperature after defrost, sometimes triggering the high temperature alarm in the middle of the night, whoever on duty will need to attend to it.

He says.....................6 times a day and fans run..........so its on a forced air defrost

I believe the coil is not completely defrosting...........
Fit electrical heaters to unit

Give us some more info