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HVACR317 – Core for Refrigeration

HVACR317 – Core for Refrigeration. Introduction to Defrost. Purpose of Defrost Systems. Defrost systems are required in low temp and extremely low temperature applications to remove the ice that builds up on the evaporator coil.

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HVACR317 – Core for Refrigeration

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  1. HVACR317 – Core for Refrigeration Introduction to Defrost

  2. Purpose of Defrost Systems Defrost systems are required in low temp and extremely low temperature applications to remove the ice that builds up on the evaporator coil. Ice is formed when warmer, humid air comes into contact with the below freezing conditions of an evaporator coil.

  3. Type of Defrost • Manual Defrost

  4. Type of Defrost Electric Defrost Shuts down the compressor and the cooling system and energizes an electric heater.

  5. Defrost The controls required to run a defrost cycle are simple: Shut down refrigeration and use hot water to melt ice on evaporator, or Defrost Clock/Time Electric Defrost Heater Over Temperature Protection

  6. Type of Defrost Hot Gas Defrost Uses a solenoid to re-route the discharge hot gas from the compressor to the evaporator bypassing the metering device and condenser.

  7. Defrost Controls The controls required to run a defrost Defrost Clock/Time Solenoid Valve Over Temperature Protection

  8. Defrost Timer Controls Initiates and terminates defrost cycle. Defrost frequency times can be preset by the manufacturer or changed by the technician. Try and keep the cycles “proportional” and keep in mind customers busy periods. Defrost may be used to return oil to the compressor on extremely low temperature applications

  9. Defrost Time Controls The same controls are used for both hot gas and electric defrost systems. You do not need different timers as they are pretty much standard. Commercial units can contain a termination (clutch) solenoid to prematurely take the control out of defrost when needed.

  10. Typical Residential Timer

  11. Typical Residential Timer

  12. Defrost Timer with Solenoid Timer Motor X 3 Source Source N Copper band 1 2 Defrost Heater Or Hot gas Solenoid 4 To Dtt To evaporator fan motor To refrigeration circuit (comp and cfm)

  13. Defrost Time Control Defrost Termination DTT Type DTT/High Limit Switch: Standard DTT which is a Defrost Thermostat, set at a high temperature to open when the ice has been melted or the coil reaches a specific temperature. The DTT de-energizes the heater.

  14. Defrost Time Control When the control terminates the defrost cycle the EFM will be delayed until the compressor can make the evaporator cold enough to switch the control back to the EFM circuit. This control prevents a “Hot Pull Down” scenario on the compressor. Hot pull down means hot gas being returned to the inlet of the compressor.

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