Compressor; Variable Capacity Compressor Control Overview - Fisher & Paykel 790 Active Smart Service Manual

6.1.5

Compressor

The compressor is turned on when cooling is required. It is switched by the power/control module sending a
low voltage frequency signal to the inverter.
The refrigerator is fitted with a variable capacity compressor (VCC). This improves energy efficiency and
maintains a more stable temperature in both the provision compartment and the freezer compartment. The
compressor windings are wired in a 3 phase star formation with the resistance between any two pins being
the same (6.4 ohms).
6.1.5.1

Variable Capacity Compressor Control Overview

The V4.2 power/control module on VCC product is identical to that on non-VCC product. The stage 4.2
power/control module senses if it is connected to a VCC compressor and uses the appropriate algorithm.
The compressor can operate at speeds between 1590 and 4500 rpm inclusive. On the Fisher & Paykel
product we operate the compressor at a select number of different speeds between 1590 and 4500 rpm to
reduce the variation in sound produced by the compressor. An electronic module/inverter connected
between the power/control module and the compressor controls the speed. (Refer Photo 6.1.5.1) This it
does by supplying a modulated DC 3 phase supply to the compressor. Warning: Permanent damage will
occur if the compressor is directly connected to the AC supply line.
The power/control module monitors, amongst other things, the refrigerator compartment temperatures (via
thermistors) and the defrost cycle, and from this information sends signals to the electronic module/inverter
to determine compressor speeds.
Whenever the compressor starts, it is run at 2200 rpm for 2.5 seconds to establish lubrication, and is then
run at 1590 rpm for a further 27 seconds before changing to any other higher speed as requested by the
power/control module. This is to provide a softer start before the compressor potentially ramps up to some
higher speed.
Whenever the fridge is plugged in/turned on, and/or after a defrost, in the first cooling cycle the control will
run the compressor, after its initial start procedure, at its maximum speed, which is 4500 rpm. The
compressor will stay at its maximum speed until both compartments have reached their cut-out temperature,
at which point the compressor will switch off and the refrigerator goes into the warm-up cycle.
In the subsequent cooling cycles the algorithm will vary the compressor speed according to the amount of
cooling required to achieve an average temperature in each compartment (as measured by the thermistors),
equal to the compartment set temperatures with a 1 hour run-time.
In low ambients where the heat load and/or cabinet usage is low, the compressor will be likely to run at its
minimum speed (1590rpm), and switch off more frequently than once every hour, similar to most non-VCC
product.
When the compressor is running at slow speeds, the evaporator may not be fully flooded, but this is normal.
Photo 6.1.5.1
Power/control
Variable Capacity
module
Compressor
Module/inverter
22