Domestic Fridges and Some Freezers Electrical Controls and Protective Parts

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Refrigerator Electrical Control Devices

Operating Controls consist of:

  • Temperature Controls
  • Defrost Timers
  • Defrost Thermostats
  • Relays
  • Some Refrigerators Electronic Board Main Assembly, Defrost Electronic Board, Electronic Controls, Electronic Refrigerator Control, Main Control Board, Main Board Assembly, Circuit Board, etc.
  • Heaters

Protective devices - such as defrost limit thermostats and overload protectors consist of thermal cut-outs.

Temperature Controls (Cold Controls, Thermostat):
a. The Refrigerator control is a thermostat which measures the refrigerator temperature and regulates the compressor (motot) running time.
- The most common method of temperature control presently used in refrigerators is the Thermostatic Control.
- The temperature control capillary tube may be fastened to the evaporator or located in the air stream to detect air temperatures.
- The temperature control is a single pole, single throw, snap action type which closes on rise in temperature. Turning the control knob, changes both the “cut in” and “cut out” settings by an equal amount.
b. The Freezer Control (electric or manual) balances the amount of cold air between the Freezer and Refrigerator compartments.

Defrost Timers:
- The defrost timer is a motor driven timer which initiates either the defrost cycle or the cooling cycle by contacts in the timer, depending on which contacts are closed.
- The defrost timer puts the refrigerator into the defrost cycle every 6 or 8 hours of compressor run time depending on the type of timer used.
- The defrost time will vary between 21 to 23 minutes depending on the timer used.
- The defrost timer is designed with a control shaft which when turned, will advance the timer into either the cooling cycle or defrost cycle.

Defrost Limit Thermostats:
The defrost limit thermostat is a bimetallic thermostat that mounts to or above the evaporator coil (an evaporator is to allow the compressed cooling chemical (R143a Refrigerant Gas) to evaporate from liquid to gas, absorbing heat in the process).
The purpose of the thermostat is to open the defrost heater circuit when the temperature around or on the evaporator reaches a predetermined temperature. The amount of heat applied and the amount of frost to be melted will determine the length of time require to bring the area at the thermostat to the cut-off temperature.
Defrost Thermostats have varying cut-off temperatures ranging from 45 °F degrees Fahrenheit (7 °C degrees Celsius), to 80 °F degrees Fahrenheit (26.7 °C degrees Celsius) – depending on the model used.

Several heaters are used in Frost-Free Refrigerators such as:

  1. Evaporator Defrost Heaters are to boil away the ice that melts from the evaporator coil during defrost.
  2. Evaporator Defrost Heaters are either carload (metal enclosed) or radiant (glass enclosed) design. The wattage and design of the defrost heater varies depending on the model it is used on.
  3. Mullion Heater, freezer case heaters and liner top heaters are used to warm up the area to prevent condensation.
  4. Drain Trough Heaters are used to prevent the build-up of ice in the drain trough. Depending on the model.
  5. The Butter Compartment Heater is used to warm up the butter compartment so that butter is slightly warmer than it would be if left in the refrigerator. Depending on the model.
  6. Evaporator Defrost Heaters to boil away the ice that melts from the evaporator coil during defrost.

Relays (Compressor Start Relay):
The starting relay is designed to remove the starting (phase) winding from the circuit after the compressor has reached a predetermined speed.

Overload Protectors:
The bimetallic overload protector is connected in series with the motor winding of the compressor. Should the current in the motor winding increase to a dangerous value, the heat developed by the passage of current through the protector, will cause it to open. This breaks the circuit to the motor winding and stops the motor before any damage can occur. Overload protectors are both current and ambient sensitive.

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