• Zanotti USA

Basic Defrost Function on Zanotti Zer0 Machine

The defrost can be initiated any time the evaporator coil is below 35F.

Defrost parameters:


“tdf” parameter has value of STD (standard) or AIR (no hot gas defrost).

“ds” parameter is the maximum time in minutes the defrost cycle will run (if Klixon doesn’t occur)

“df” interval in hours between the beginnings of defrost cycles


Defrost is initiated automatically by the defrost timer (parameter dF), or manually by pressing the manual defrost switch. The defrost timer initiates when the defrost termination switch closes, the evaporator coil is below 35F, AND the unit is in cool mode.


The defrost relay (K11) energizes the defrost solenoid valve, and de-energizes the evaporator and condenser fans. Defrost will continue until the evaporator coil temperature rises to 46F, causing the defrost termination switch to open ending the defrost cycle or the maximium time limit has been reached (parameter dS)


To start manual defrost:

Press for the defrost button (melting snowflake) 5 seconds to start the cycle. When LED on the button is on, defrost is running.


Testing Defrost:

To test the defrost system, run the unit on cool until the evaporator coil temperature is below 2.2 ± 3.0° C (36.0 ± 5.4° F) and press the manual defrost switch.


If the unit doesn’t shift to defrost cycle go to step 1.



1. Check the evaporator temperature.

Be sure the evaporator temperature is actually below 2.2 ± 3.0° C (36.0 ± 5.4° F), otherwise the unit will not defrost. Use a test thermometer to check the evaporator temperature.


2. Check the defrost termination switch. If the unit fails to defrost, place a jumper wire between the 27 and 28 wires at the defrost termination switch. Press the manual defrost switch. If the unit shifts to defrost, the defrost termination switch is defective.

If the unit does not shift to defrost, check the fuse FSS.


3. Check the fuse FSS

If voltage on wire 38 is not present, check K11 relay.

If voltage is correct, replace the solenoid valve YS.

If voltage mentioned steps are all respected, replace the printed circuit board.


Advice – The efficiency of the defrost is inextricably linked to the drain water hoses


  • The steepness of the discharge is smooth enough to ensure discharge

  • Periodically check the outflow of water from the drain hose

  • Minimize opening the doors, and turn the unit off when loading and unloading

  • In the case of intensive use regularly check the accumulation of ice in the evaporator and periodically run a defrost to ensure the complete melting of ice.

Contact Zanotti HQ

 856-393-7230

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