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Product Overview - Bosch SHI 4302 Repair Manual

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Product Overview

The Bosch dishwasher utilizes a two motor system with separate Circulation and Drain Motors, and a
Flow Through Heater controlled by a Flow Switch and NTC Thermistor. With some models also having
the advanced logic feature of an Aqua Sensor turbidity measuring devise, Fig. 2-1.
• A two motor system allows each motor to be designed for a single function, thus reducing overall
size and energy consumption. While also reducing operating noise.
• The Flow-Through Heater allows a shorter heating cycle since all water must pass through the
Heater, increasing water temperature by approximately two degrees a minute. To protect the
heater from dry fire, the Flow Switch will not allow the Heater to activate unless water is flowing.
• Water temperature is controlled by the NTC (negative temperature coefficient). As water
temperature increases the NTC records the decrease in resistance. The Control Unit Logic Board
measures this resistance change and allows the program to advance once the correct
temperature (resistance level) is reached.
• The Aqua Sensor turbidity measuring device, which is available only on select models, evaluates
the pre-wash water using a beam of light and a pick-up sensor. If the beam passes easily through
the pre-wash water then no additional wash water is added. If the beam cannot pass through,
then the pre-wash water is drained and a fresh fill is added for the main wash cycle.
The heated water then advances through the system via a four level wash system that uses both an
upper and lower spray arm as well as an overhead sprayer, Fig. 2-2.
Upper Spray Arm
Lower Spray Arm
Impeller Cover
Drain Motor
Fig. 2-1
Aqua Sensor
Flow Through Heater
Flow Switch
Circulation Motor / Pump

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