Fisher & Paykel RF175W, Service Manual

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6 ELECTRONICS SECTION
The control system consists of the power/control module located in the unit compartment of the
refrigerator, and various sensors and actuators controlled by the power module. The function and
brief description of each of these units is defined below.
Power/control module, display module, compressor, defrost heater, ambient heater, produce
compartment fan, freezer compartment fan, light, temperature sensors and door sensors.
6.1 Function Overview
The purpose of the power/control module is to turn on the compressor, which cools the evaporator,
then to use the fans to efficiently cool the compartments. Both fans turn on with the compressor.
The freezer compartment (FC) fan is kept at a constant speed while the provision compartment
(PC) fan is regulated to provide the cooling for the PC compartment, which operates independent
of the FC compartment in controlling its temperature. The function of the microprocessor in the
power/control module is to provide independence of both compartments to their set temperatures,
although the environment of one compartment effects the other as they are linked by the ducts as
can seen by the diagram of the internal air flow of the cabinet (refer to Section 7.8).
6.1.1 Power / Control Module
This module is the electronic brain and control centre of the refrigerator. It contains a
microprocessor, support circuitry and switching devices. The power/control module controls the
provision compartment (PC) and freezer compartment (FC) temperatures by sensing the
temperature and door state and operating the compressor and fans accordingly. This module also
houses the alarm beeper.
The speed of the fans is controlled by pulse width modulation (PWM). The power/control module
controls the fan motor speeds by driving them with short pulses. These pulses vary in duration to
change the speed of the motor. The longer the pulses, the faster the motor turns, and vice versa.
The micro controller in the power/control module uses its internal memory for control; its ROM
(Read Only Memory) for program and fixed constant storage including tables, the RAM (Random
Access Memory) for variable storage and access. It uses an external Electrically Erasable
Programmable Read Only Memory (E2PROM) for storage of variables and history data, which is
retained even when the power is turned off.
The power/control module contains a special type of memory device call an E2PROM. The
information on the refrigerator operation, faults and diagnostic information is stored in this memory.
They include the temperature setting, the history of FC, PC temperatures (approx 18 hours),
defrost history (the last 12 defrosts) and fault history. This will help the service person find and
remedy the cause of failure. All this memory will be retained even when the fridge is disconnected
from mains power supply.
The beeper is used to signal prolonged door opening and other fault conditions:
1. The PC door alarm sounds if either PC door is left open for 90 seconds and the FC drawer
alarm sounds if the drawer is left open after 60 seconds. Both PC & FC alarm will sound every
30 seconds until the door is closed.
2. If the doors and drawer are left open longer than 5 minutes, the alarm will sound continuously
and the PC and/or the FC light will turn off. The alarm will stop with the closing of the doors
and drawer. The light is only reactivated by closing and opening the door and drawer.
3. All electronic faults, when detected, will sound the alarm when the door is opened and the fault
will be shown on the display.