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Ntc Operation - Bosch SHI 4302 Repair Manual

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52

NTC Operation

Fig. 14-1
Located on top of the Heater Assembly is the NTC (Negative Temperature Coefficient), Fig. 14-1. The
NTC uses resistance to control wash and rinse water temperature and is connected with two green leads.
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.
Service note: The SHU 30** and SHU 40** models do not use an NTC, but utilize a standard, normally
open thermostat (bi-metal).
Also combined within the NTC (or standard thermostat) is a High Limit Safety Thermostat, connected
with red leads. The normally closed high limit is set to 185° Fahrenheit and is self-resetting.
Service tip:
The NTC can be checked without removing the dishwasher by measuring its resistance at
the Control Unit. Using the appropriate wiring diagram, locate the two NTC leads. The
resistance at room temperature should be approximately 55k Ohms.
An extremely high, low or no Ohm reading will usually indicate a faulty NTC.
H

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