The system is inefficient and running constantly.
This is only true for contact sensing cold
controls.
This requires explanation because it initially seems
backward. Nearly all cold controls monitor air temperature in the
fresh food section. They shut off at about 36 degrees. There is only
one evaporator within the freezer compartment and a portion of the
cold air is diverted into the fresh food compartment. On a few,
mostly older designs, the evaporator is split between the freezer and
the fresh food compartments. Freon first evaporates on the freezer
and then circulates onto the fresh food evaporator. If the system is
low on freon or inefficient, little freon will make it to the fresh
food side. On this design, often the cold controls is mounted right
on the fresh food evaporator and shuts off at a surface temperature of
10-15 °F.
Normally, air flowing over the small 15 °F evaporator
will balance out with 36 F fresh food. A system in the early stages
of failure may cool off the evaporator, but not cool it enough to
satisfy the cold control. The fresh food temperature may slowly drop
below freezing as the cold control futilely waits for the surface of
the evaporator to get down to 15 °F but it may never go below 20F.
The compressor will run constantly and eventually all the food will
freeze.
Years ago, when these systems were popular, some
mechanics exacted a temporary fix by removing the surface contact
control and installing an air sensing control like the ones used
today. Depending on the rate of deterioration of the freon system,
this solution would work for years; more often it only lasted a few
months.
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Troubleshooting Refrigerators
Diagnostic System
