Bosch SHE55P Repair Manual page 22

4.1.17.1 Reed switch dispensers
The white plastic linkage opens the detergent dispenser door,
then cocks in place to dispense rinse-aid when the wax motor
operates again. After the 2nd operation, the linkage resets for
the next wash.
702_58300000148618_ara_en_a
4.1.17.2 Optical dispensers
Optical dispensers are connected differently and can't replace
reed switch dispensers.
TIP: It's possible for some clear rinse-aid brands to not diffuse
light adequately to show rinse-aid isn't needed.
With rinse-aid
present, the optical
receiver senses a
diffused light beam.
When rinse-aid has
run out, the optical
receiver senses a
strong light beam.
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