One of the issues with the 777 is that the temperature sensors in the cabin suffer terribly from clogging with dust/carpet/blanket fibres, and never get cleaned.

If you look above the A/B seats, I think second row down, there is a small grill in the curves section below the lower pivot edge of the overhead lockers, it is a sort of rounded corner rectangle. The temperature sensor is in there and is often full of dust. Very simple to rectify with a teaspoon and a cloth... ^

And, thus being, when it is clogged, the system can not read the temperature correctly, and will keep heating the cabin as it has not reached temperature on the sensor...