General Information; Most Often Misdiagnosed Problem - Viking VUWC140 Service Notebook

VIKING RANGE ALL-REFRIGERATION MODELS
VUWC140/150—VUAR140/150—VRBD—VUBD
The all-refrigerator product line encompasses traditional all-refrigerators, beverage storage all-
refrigerators with temperature barriers to create different temperature zones, refrigerator
beverage dispensers, and wine storage refrigerators.
All these models employ an evaporator plate for cooling the cabinet interior and an evaporator
plate sensing thermostat to control the compressor operation and therefore, the interior
temperature.
A cycle defrost system is also used on all these models. The plate sensing thermostat is designed
such that at the end of each compressor run cycle, the evaporator plate must "warm-up" above a
freezing temperature before the compressor will restart. During this "warm-up" period, any
accumulated frost on the evaporator melts and drips off the evaporator plate into drip channels
and a drip tray. From the drip tray, a drain tube carries the defrost water to a pan in the
mechanical compartment. There, condenser fan air movement and compressor heat evaporate
the water.

Most Often Misdiagnosed Problem

Sealed refrigeration system leaks are the most often misdiagnosed problem on the Viking all-
refrigerator models. The interaction between the evaporator sensing thermostat, the mounting
location of the thermostat thermobulb, and a low refrigerant condition within the evaporator,
yields a condition in which the cabinet interior air temperature drops below freezing and stored
commodities become frozen.
End users respond to the colder interior temperatures by adjusting the thermostat knob to a
warmer setting, until they reach the warmest available. When their stored commodities continue
to freeze at the warmest setting, they call for service. The end user states the problem as "the
thermostat is set at its warmest setting yet everything inside freezes."
This leads most service technicians to suspect a bad thermostat. When the technician examines
the unit and finds that the compressor runs continuously, the tentative diagnosis is confirmed.
The technician's diagnosis is that the thermostat is not functioning properly and he replaces it.
When this does not correct the problem, often the thermostat is replaced a second time because
the technician believes the first replacement thermostat might have also been defective. By this
time, the end user is upset because the technician cannot repair his unit and the technician is
contacting the Viking Customer Services Department to inform us that he has received two
"defective" thermostat service assemblies!
What a mess! Let's back-up to the beginning to determine where this service call went wrong.
When the end user stated the problem as "the thermostat is set at its warmest setting yet
everything inside freezes", the technician automatically thought, "too much run time", probably
bad thermostat. But the problem was actually a low refrigerant charge or leak. Typically, when
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