Electronics Section; Diagrammatic Overview Function Description; Control & Peripheral Functions; Power/Control Module - Fisher & Paykel RF201A Service Manual

6

ELECTRONICS SECTION

6.1

DIAGRAMMATIC OVERVIEW FUNCTION DESCRIPTION

The electronic system consists of several parts:
Power / control module, display module, compressor, defrost heater, ambient heater, produce compartment
fan, freezer compartment fan, light, temperature sensors and door sensors.
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 produce 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.
6.2 CONTROL & PERIPHERAL FUNCTIONS
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

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
motor speed 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 (E 2
PROM) 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 E 2 PROM. The information on
the fridge 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.

Door Switches

"Reed" switches are used to detect the opening and closing of the doors. Small magnets are built into the PC
doors and FC drawer, which activate the reed switches. The reed switches are encapsulated within a plastic
housing, which is clipped under the plastic covers on the base and cross rails.

Defrost Heater

A heating element is used to defrost the ice accumulated on the evaporator. The defrosts are adaptive to the
usage and environment and are controlled by the power / control module and sensed by the defrost sensor
located on the evaporator chassis registering 46
o
F before terminating the defrost heater element. Previous
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