Electric Defrost

[iceman007]

Does anyone have an idea of why during defrost cycle on a ARNEG Dairy Chiller temperature is staying between 11 & 12 degrees and sometimes rising to 20? The cabinet defrosts 3 or 4 times a day and then pulls back down. It has a remote condensing unit running on 404A suction pressure 34 PSI gives me an evaporating temperature of about -17 to maintain refrigerated temperature.

When it was installed, I believe the customer was told the thermostat should read no more than 5 degrees. Is there a part such as a bimetallic klixon that can be replaced to cure this? Electric defrost is not my strongest point but I know the defrost cycle is lasting about 45 minutes to an 1 hour.

[Mark]

Hi iceman
Usually for safety, a klixon and or stat is fitted in the heater circuit.
What controller is the cabinet using?standard mechanical stats and timeclock?.
Defrosting can be controlled by terminating the heaters on coil or air temperature or time,a klixon in the coil would control heaters and be a back up if timeclock etc failed .As well as preventing high rise in product temperature.
45 minutes to 1 hour is too long a defrost period,maximum defrost time is 30 minutes for this set up, if the heaters are staying on for this duration then the case temperature will rise excessively.It needs some control and or adjustment.By means of klixon and or stat.
Best regards
Mark

[Mark]

iceman
Just read your thread again the air temperature in the case will momentarily fluctuate when on defrost what ever defrost method.
Electric defrost,gives a quicker air/product temperature rise and would need something to protect against excessive heat.
Where as off cycle or air defrost is a more gentle defrost method.
The cabinet temperature in fact will rise on defrost, however for how long and to what temperature can only be governed by how it is controlled,and the other factors which make up the cabinet product temperature.
Kind regards Mark

[chemi-cool]

hi iceman,

got to agree with mark.

please check where the temp controller reads the temp, it might be too close to the heating element.

another trick that can calm your cleint is to set the controller to hold temp while on defrost so even if air temp inside rises, the reading stays as when it started the defrost cycle

chemi

[iceman007]

Hi Mark & Chemi

I had not seen the cabinet when I posted my thread, but took the info from the technician on site.
Went and had a look. Temperature was 14.8 at the end of the defrost cycle. Standard mechanical stats. One thermostat for cabinet temp, and one coil stat for defrost end. Defrost on time clock. Set for three defrost cycles per day-30 minutes each wuth 5 minute time delay on evaporator fans.
Decided to set the defrosts for a higher frequency and half the time so it will defrost more often, but the temperature will not rise as much. Standard control box is in roof space-took ages to find, has the time clock, dials for thermostat and defrost overload etc.
Hopefully problem solved
Many Thanks
James

[iceman007]

Problem not solved.
The thermostat is not close to the heating element.
The case is rising to about 9 degrees at the end of the defrost cycle.
I shortened the cycle and doubled the frequency of them to attempt to keep the temperature under control.
The control box and timeclock is in the ceiling space and consists of 2 thermostats, 1 for the temp settting and a defrost overload. There is also a defrost end thermostat wired in. I can't set the temperature to hold during the defrost cycle, as it's quite a basic control system, but feel that I must be overlooking sonething somewhere. I can't think of what else it could be. The rest of the system is operating normally.

Regards
James

[chemi-cool]

hi james,

I would throw away all the mechanic controls and install an electronic temp controller such as eliwell 974 or any equivalent one using two sensors.

its a + temp so there is not too much ice on the fins cut the defrost time to 10 minutes and see how it goes.

also check that regulating sensor is in the return air near the fans.
the hot air from defrosting usually goes up at the back.

chemi

[dill]

The art to defrost is to have as little as possible and as short as you can get away with. By that I mean limit your defrost periods and lengths to the shortest you can get away with to keep the coil clear of ice. I have been in supermarket refrigeration for over 25 years and by far my biggest enemy has been water wether it be leaking on the floor,clogging coils or sitting in expansion valves. I have found that in most cases a ten minute dfrost twice a day is enough. Keep the times of defrost to early morning and late on so as to deter nosy customers and frantic staff. Make sure you start with a fully defosted coil before setting yor times and dont forget to look out for the reasons behind ice build up on coils ie. Air blowing in from AC systems, open doors, faulty door seals, faulty solinoid coils (favorite in radford cabinets) poor drainage ect. James the list goes on, but keep your chin up as you are not alone as the man who can erradicate water problems from refrigeration hasn't been born yet. best wishes dill.

[Andy]

Hi Iceman 007
If you have less defrosts for longer periods, what happens? I prefer this as there are less pulldowns.
Not short of gas causing excessive de-humidification
No heaters blown maybe the heater that would best terminate the stat is blown.
Fans off cycling and staying off during defrost
No dirt in the coils or ducts, again causing extra, not designed for de-hum.
No air con ducts or other sourses of hot air causing extra load on the cabinet, with extra moisture to remove during defrost

Take heart the answer is out there from memory aren't the Arneg fins quite closely spaced on the cabinets?

Kind Regards, Andy.

[iceman007]

Hi all,

I had been thinking about replacing the controls for something like an Eliwell Chemi.
The fins aren't spaced close together Andy, well no closer than average. I cut the defrost time to 15 minutes, and during the time the space temp,(it's an open fronted cabinet with remote condenser) is going from about 1 degree to 9 or 10 degrees. I think I'm going to move the thermostat lower down the cabinet, and cut the defrost to twice a day for 10 minutes, as the saturation point for evaporation is at around minus 10 degrees. Initially I had thought about taking the gas out to check the charge, but noted that on the equipment plate, there's no charge information, but I concluded that the pressures for both units is identical.
Anyway, I think I'll try cutting the defrost down a bit more and see if that works, as 30 minutes a time is probably a bit too much, due to the fact that the coil is probably defrosting during the off cycle, which is for about 5 minutes every 15 minutes. Thanks for information Dill, that was helpful- I wish I could find the solution to eliminating moisture- I'd be rich.
Many Thanks
James

[Gary]

Hi all,

I had been thinking about replacing the controls for something like an Eliwell Chemi.
The fins aren't spaced close together Andy, well no closer than average. I cut the defrost time to 15 minutes, and during the time the space temp,(it's an open fronted cabinet with remote condenser) is going from about 1 degree to 9 or 10 degrees. I think I'm going to move the thermostat lower down the cabinet, and cut the defrost to twice a day for 10 minutes, as the saturation point for evaporation is at around minus 10 degrees. Initially I had thought about taking the gas out to check the charge, but noted that on the equipment plate, there's no charge information, but I concluded that the pressures for both units is identical.
Anyway, I think I'll try cutting the defrost down a bit more and see if that works, as 30 minutes a time is probably a bit too much, due to the fact that the coil is probably defrosting during the off cycle, which is for about 5 minutes every 15 minutes. Thanks for information Dill, that was helpful- I wish I could find the solution to eliminating moisture- I'd be rich.
Many Thanks
James

Does the fan shut off during defrost? Does the sytem pump down during defrost? Is there a fan/limit switch? Is the defrost terminated by time or temp?

[iceman007]

Hi Gary

Think I've sorted it out now. Yes the system pumps down, but I noticed that the evaporator fans were still running. I have to wait a couple of days for the customer's head office to give me the go ahead. I don't know yet how the fans are wired to the timeclock. The funny thing is that they only started complaining about this a few days ago. The kit's been installed over 18 months.

Regards
James.

PS- Your troubleshooting books:how much do they cost and will you ship to the UK?- Never to late to learn !!

[Gary]

Products and prices are listed here:

https://www.merchantamerica.com/tmethod/

I offer a flatrate shipping option which is considerably cheaper, albeit a little slower, than UPS shipping. It generally takes about a week to Europe. When you get to the shipping options, just select "flat rate".

[iceman007]

Thanks for the information Gary. I'm annoyed with myself. This is a problem I should have been able to diagnose in minutes, but due to other personal issues have been a bit clouded in judgment over the last couple of days or so, I have to return and rewire the fans.

Regards
James

[Mark]

Ok but the evaparator fans running on defrost is not unusual for these type cabinets......... .
Ive seen arneg cabinets fitted with stats in the air-off that limit the threshold of the heater/s .
Take the cabinet apart and look where the heater is situated and what type of heater fitted (it was a rod heater).
Best regards
Mark

[Abe]

So it was the bleeding fans staying on during defrost, huh Iceman??

Well done Gary.......

[iceman007]

It was the evaporator fans. They've been wired to work through the timeclock. 2 thirty minute defrosts per day, and 5 minute fan delay. Problem is all sorted out. Thanks to all for the help.

Regards
James

[Mark]

They must be different to the arneg cases i work on

Best regards
Mark

[chemi-cool]

Hi Mark,

Most of these + temp cabinets use air defrost. Maybe that explains the fan working through defrost cycle

Chemi

[Mark]

Even when using electric defrost the fans are hard wired from the fuse/mcb......... on some cabinets...