Instead of having the fridge on constantly. Just check it once per cycle. A clock sensor on 1% duty cycle turns the power shut off on which powers up the fridge. The clock sensor signal also goes to the set input of a memory gate. After being powered on the fridge then sends a signal out if it's full. We delay the signal with a 2s buffer gate before sending it to the reset input of a memory gate. The output of the memory gate will now be negative if the fridge is full, and will remain so until next cycle where the fridge is checked again. Likewise the output of the memory gate will be positive if the fridge is not full, and will remain so until checked again next cycle.