Frigidaire sells a $29 5303918301 laminated "garage heater kit," with
2 wires that wraps around the cold control of a fridge to allow it to
work in to work in a cooler room, down to about 40 F.

It apparently heats the thermostat to fool the compressor into turning on,
even if the fridge compartment is cool enough (eg 40 F in a 40 F room.
Without this kit, the compressor does not run often enough to keep ice
cream from melting.

How does this work, exactly? Is the heater always on? Is it just adding
enough heat to the fridge compartment to make the compressor run long
enough to keep the freezer compartment frozen? If so, why is it
wrapped around the cold control, vs somewhere else in the fridge box?

I just bought an 18.2 CF Hotpoint fridge. I'd like to cover the outside
with 2" foamboard and run it in a cool kitchen to reduce the energy used
from 480 kWh/year to 240 or so, but Hotpoints don't come with these kits.
Would leaving the light on all the time in the fridge compartment do
the same thing? Is there a more energy-efficient way to do this? Warming
the whole fridge box takes more power than just warming the thermostat.

Nick