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joe magee
01-06-2012, 02:01 AM
Reach in frozen food case coil is frosting up over a period of a few months.

Refrigeration contractor states that Voltage is not enough at case. The defrost heaters are rated @ 220 volts and draw 16.83 according to data plate. I was reading 197 volts at case in defrost and 21.5 amps.
Now according to ohms law wattage would be 3702 @ 220 volts and 4235 @ 197 volts.

Are the heaters warmer @ 197 volts?

So would increasing the voltage cause the heating elements to burn hotter? And why?:)

Slatts
02-06-2012, 11:30 AM
I'd be less woried about the temperature of the heaters and more interested in the defrost duration, termination type and temperature and regularity (how many per day).

mad fridgie
02-06-2012, 12:02 PM
Would say you get a short problem!
High amp, low voltage, poor heat "short"

monkey spanners
02-06-2012, 12:30 PM
Less volts = less amps so lower wattage. If it worked the other way then with 0.000000001V going to them you'd have eleventy hundred Kw worth of heating!

Would be worth ohming out all the heaters, suspect theres a duffer in there somewhere.

joe magee
02-06-2012, 04:41 PM
Case temp, super heat, defrost times termination all have been looked at. Term temp is 60 defrost time 45 once a day ,pretty standard on a glass door frozen food case. Set point is -11. Walmart does not use the defrost termination klixon supplied with case. They terminate defrost on the supply air temp sensor. I like that idea in a med temp case with airflow but not for a frozen case. Be that as it may thats what they use.

install monkey
03-06-2012, 12:03 AM
if the defrost settings are normal to other cases then id be looking at airflow circulation,location of the supply air sensor and comfirm actual and display temps, also are they overloading the cabinet?

Slatts
03-06-2012, 12:42 AM
As the fans are off during defrost the sensor would have to be located close to the coil to be of any use in defrost termination, as you've noted.

Your heater currant isn't reading higher than the data plate rating because you're tonging the drain pan heater with the defrost heaters?

Also, is the defrost terminating off minimum, maximum or average temperature?

By the way, what's the make and model of the cases?

I assume that you've had a look at the door seals and torsion bars?

joe magee
03-06-2012, 04:00 AM
It's actually a line up. One five door four four door Reach ins. All cases are having same issue. Sorit and solenoid holding during defrost. Cases are only a year old. It's been happening since day one. drain pan is included in spec. Defrost is 60 degree term temp and 45 min. Runs full defrost time.

Slatts
03-06-2012, 04:14 AM
I'd try uping the defrost to 50 min and defrosting all the coils then see how it performs.

cold.man
03-06-2012, 12:43 PM
i would put an extra defrost in aswell.
def time 45mins....def term temp leave at at temp it wont reach so it defrosts on time rather than temp.

joe magee
03-06-2012, 04:31 PM
Thanks for the input. WalMart is a different breed. If the cutsheet says 45 min with a 65 degree termination you better give them a good reason why they need to change it. I always tell customers that the cutsheet numbers are starting points and there are other factors that need to be considered. This store is a smaller store without dehumidification so I might be able to have them add another defrost or perhaps add time to the exsisting one.
Store conditions were ok but the problem is WalMart and Target use setbacks and open economizers at night when product is being stocked.

Slatts
04-06-2012, 09:47 AM
That leads to my next suggestion.

Blame the A/C people:o

Unless of course you look after that as well, in which case forget that I said that.

Bottom line, if the heaters are all working and the defrosts are taking place at the designated times for the designated durations and the cases seal properly then there's not much more you can do without stepping out of their parameters.

The condensate drains are trapped?

Gary
04-06-2012, 05:58 PM
Defrost is 60 degree term temp and 45 min. Runs full defrost time.

There's the problem. The defrost should always be terminated by temperature. The timer is there for back-up only. If the heaters are working properly, lengthen the time duration.