Hi,

MSD2356

That is part of a full model#.

It is running all the time and the
freezer is far too too cold but the
refrigerator temperature appears
normal (possibly on the warm side)

Make sure there is no frost building up on the back wall of the
freezer.

Can anyone provide info on how
temperature is regulated in a typical
side by side setup.

Nothing is typical

But this may help...a copy:

*If you open the fresh food compartment of your fridge (the non-freezer
compartment), you will most likely see two different controls. One
refers to the refrigerator temperature and the other refers to the
freezer. Different manufacturers use different wording, but the idea is
the same.

The first thing you need to know in order to understand what these
controls really do is that all the cold air in the entire refrigerator
is made in the freezer compartment. A portion of that cold air is then
blown into the fresh food compartment. How much cold air gets blown in
is controlled by the "freezer" control, which is really just an air
baffle that opens or closed to let more or less air into the fresh food
compartment. The "refrigerator" control is actually a thermostat that
feels the temperature inside the fresh food compartment and turns the
compressor on and off according to the temperature that the thermostat
feels.

Let's run through an example. Suppose you decide that your ice cream
isn't hard enough. You adjust the "freezer" control to make your
freezer colder. What you're actually doing is restricting the amount of
cold air that gets blown from the freezer into the fresh food
compartment and so keeping more of the cold air in the freezer. As a
result, the freezer will get colder but also the fresh food compartment
will tend to get warmer because its cold air supply has been
diminished. The "refrigerator" control (the thermostat) will feel this
increase in temperature inside the fresh food compartment and will keep
the compressor running longer in order to maintain the temperature
setting on the "refrigerator" control. So, you can see that any change
you make to one control will affect the other.

Many people then wonder, "Well, how do I know what the correct setting
on the controls should be?" Since the temperature inside a refrigerator
will vary according to lots of external factors such as frequency and
duration of door openings, it is impossible to say where your controls
should be set all the time in order to maintain a desired temperature
in the freezer and fresh food compartments without knowing the actual
temperature inside both compartments. For this reason, you should place
two thermometers in your refrigerator: one in the fresh food
compartment (the big one) and the other in your freezer. The controls
should then be adjusted to achieve -5 to +5=BAF in the freezer and
between 36 and 38=BAF in the fresh food compartment.

Keep in mind, too, that it takes 24 hours for any change in the
controls to work through the system and reach steady state so don't
look for instantaneous changes in temperature when you make control
setting changes. Knowing the actual temperature inside your
refrigerator compartments is also a great way to save money on your
power bill since you can adjust the controls to avoid running your
compressor longer than needed to keep your food cold.*

jeff.
Appliance Repair Aid
http://www.applianceaid.com/