View Full Version : Electric Defrost loads on Compressor configuration

05-08-2011, 06:20 PM
Hello, I'm a newbee (non-engineer), and currently ordering some condensing units. I was asked what the loads(V and Amp) were for the electric defrost.

Can anyone explain how the electrical loads on the refrigeration cases will affect the Compressor function? Since they are on different power sources(120 vs 220), it seems odd to me.

Thanks for the help.


06-08-2011, 02:36 AM
Hi Bryanwa

You should find the compressor cycles OFF during defrost

When the defrost ends and the compressor restarts it will be under additional load from the heat of the hot evaporator, drawing more amps

As the evaporator temperature drops so does the suction pressure which in turn lowers the load on the compressor and the amp draw

08-08-2011, 05:09 AM
Thank you Chillerman! That makes total sense now.

Roberto Cancio
10-08-2011, 10:01 PM

I wonder what is the optimal duration and period for electric defrost chamber -25 C.


10-08-2011, 11:30 PM

I wonder what is the optimal duration and period for electric defrost chamber -25 C.


Hi Roberto

Defrost should be terminated by temperature and backed up with a timer in case the klixon fails

How often is going to depend upon how often the evaporator starts to ice & restrict air flow

You can set a timer to suit your needs or better still use a differential air switch

11-08-2011, 01:12 AM
Hi Bryanwa,
the case manufacturers with specify the heating/defrost power requirements. Example 3 phase 220vac x 3 x 60Hz,, 120vac x 1 x 60Hz., xyz watts. How they configure the elements will be prewired before delivery. Some suppliers can have star connected with 3 phase for low voltage, others across the line for high voltage. Or single phase . They will always state Amps supply and voltage supply.
Defrost frequency per 24 hours will effect actual refrigeration requirements, while defrosting the system is not cooling, so selection of condensing units is critical. Defrost loadings has to be added to total loadings per 24 hours, compressor run times etc..
Example: Low temp case @ -18'C holding. calculated loading per 24 hrs 500Kw + [ 6 defrost per 24 hrs @ 60 minutes per/5Kw per defrost] 30 kw + 10% safety margin = 500 + 30 + 530/10 = 583 Kw. Required run time = 16 hours per 24. So 583/16 = 36.50 Kw refrigeration capacity minimum required.
Hope this helps