My fridge on propane has a usual range of 32-40 degrees
over night and day.  A super hot day will send it up a
little more.  Running a fridge fan inside keeps it much
more even, I recently discovered.  This is with my
thermostat knob about 9:30 position.  Any higher and I
freeze the stuff overnight.  Of course, every fridge
probably has a slightly different thermostat calibration.

If you turn on 115V with propane, there should be no
real effect, since the thermostat controls both and the
extra heat during the cooling cycle should be wasted--
or the fridge is underdesigned.  On 12V, the effect is
to run the fridge constantly, since the thermostat doesn't
control the 12V heater.

Some have recommended running propane and 12V initially to
speed cooling, but, again, I think the fridge design should
be to have maximum cooling on any one of the three modes and
so extra heat would be wasted.  A fridge fan inside does
certainly speed initial cooling, in my observations the last
few months.

                                Richard A Jones
                                Boulder, Colorado