Maytag Built-in Refrigeration, Manual

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48
Variable Capacity Compressor
The sealed system in the Jenn-Air
®
Luxury
™
Line of
Refrigerators incorporates Variable Capacity Cooling.
Most conventional refrigeration systems use single
speed compressors. The capacity is constant and the
controls meet the cooling demand by cycling the
compressor on and off. With a Variable Capacity
Compressor (VCC), the compressor speed is adjusted to
better match the cooling requirements of the refrigerator
itself. This results in longer run times at a lower
capacity.
Since the most stress and instantaneous energy usage
occurs while a motor is starting; by eliminating the
number of times the system cycles off, the stress on the
system is minimized. The other advantage of operation
at a lower speed is reduced sound levels. A compressor
running at a lower speed will produce less noise in the
vicinity of the refrigerator.
The Main Control Board uses information from all six
thermistors to determine the compressor speed. The
compressor will always start at high speed but will
quickly adjust to the calculated capacity after starting.
The compressor motor is a three-winding motor. These
three windings are powered by the Compressor PCB
(Printed Circuit Board). The Compressor PCB is
controlled by the Main Control Board.
The Compressor PCB is supplied power from the AC
line cord. This AC power is converted to DC power on
the board. The DC power is sequentially switched to the
three motor windings to drive the compressor. By
adjusting the speed at which these three windings are
switched, the speed of the compressor can be adjusted.
The switching speed is determined by the Main Board and is communicated by sending a
variable frequency signal from the Main Board to the Compressor PCB. This signal can
range from 150 cycles per second (Hz) to 53 cycles per second. The resulting compressor
speed will adjust between 4500 RPM to 1600 RPM.
Servicer’s Note
The Variable Capacity Compressor looks very similar to a standard single speed
compressor. The three terminals on the outside of the compressor are arranged the same
with either style of system. When taking resistance measurements around the terminals
on the outside of the case do not let the different motor design cause confusion. The first
check is to still verify that there is NO continuity to the case itself. This is the same as
with any standard compressor. When checking between the three terminals, the resistance