Alec wrote:
I cannot see why an ammeter should not be in the power line. You only need
to measure the current once.

This is certainly not true for all refrigeration systems. It may be
that a Danfoss system with a simple evaporator has a constant draw,
but my larger DC holding plate system varies by 50% in draw, and 80%
in total load.


To measure the time it is on, assuming a 12v fridge, the cheapest way is to
get an "old" 12v analog (mechanical movement) car clock and wire it after
the thermostat, this will then give you the time the fridge runs. A car
scrapyard is the place to visit.

neat trick.