Compressor; Variable Capacity Compressor Control Overview; Built-In Electronic Protections (Within The Module/Inverter); Compressor Start-Up - Fisher & Paykel RB90S64MKIW Service Manual

9

COMPRESSOR

The CoolDrawer is fitted with a variable capacity compressor (VCC). This improves energy efficiency and
maintains a more stable temperature within the compartment. The compressor windings are wired in a 3
phase star formation with the resistance between any two pins being the same.

Compressor Overload

The VC compressor is protected by an overload mounted under the compressor terminal cover. The
overload is part of the compressor harness as the leads are spot welded to the overload. This means that if
a replacement overload is required, an overload kit will need to be connected to the harness by means of a
molex plug.
9.1

Variable Capacity Compressor Control Overview

The compressor can operate at speeds between 1250 and 3800 rpm inclusive. On the Fisher & Paykel
product we operate the compressor at a select number of different speeds between 1250 and 3800 rpm to
reduce the variation in sound produced by the compressor. An inverter is part of the power/control module
and controls the speed of the compressor. It does this 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 compartment temperature (via thermistors)
and the defrost cycle, and uses this information 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 1150 rpm for a further 27 seconds before changing to any other higher speed as requested by the
power/control module.
Whenever the appliance 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 3800 rpm. The
compressor will stay at its maximum speed until the drawer has reached its cut-out temperature, at which
point the compressor will switch off and the drawer goes into the warm-up cycle.
9.2

Built-In Electronic Protections (Within The Module/Inverter)

9.2.1

Compressor Start-Up

In the event of any anomaly occurring during compressor starting, the control will wait 30 seconds before
repeating the start-up. If the compressor doesn't start after 3 trials, the control will wait 5 minutes before
repeating the start-up procedure (this condition may be when pressures are not equalised between suction
and discharge sides in the refrigeration system, eg; after an interruption in the mains supply).
9.2.2

Overload Detection And Protection

The control can detect an overload condition by monitoring the current consumed by the compressor. If
overload is detected, the control reduces the current by reducing the speed of the compressor until the
overload disappears, when the speed will return to the required value.
If the overload increases, the control will continue to decrease the current until the minimum speed of 1590
rpm may be reached, at which point the compressor may "stall", and the control will return to the start-up
procedure.
9.2.3
Compressor Overload
The VC compressor is protected by an overload mounted under the compressor terminal cover. The
overload is part of the compressor harness as the leads are spot welded to the overload. This means that if
a replacement overload is required, an overload kit will need to be connected to the harness by means of a
molex plug.
9.2.4

Power Limitation (Temperature Protection)

The control limits the power supplied to the compressor to 200 watts to keep all electrical components below
a safe operating limit. The power is limited in the same way as the current in the overload protection.
9.2.5

Short Circuit Protection

In a case where a short circuit occurs, (eg; motor winding damage, connection faults etc), the same current
limiting control is actuated to reduce further damage. In the case of a major failure, a fuse within the inverter
will break the current supplied to the control. This fuse cannot be replaced in servicing.
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