The chart doesn't seem to make sense. Sure, the maximum capacity of the system declines as the outdoor temperature drops. But, does the power draw of the compressor also drop? I fail to see why that would be so.
The compressor may have a limited maximum RPM, and when it is colder outside, the maximum refrigerant temperature may be colder. Perhaps it takes less power to compress colder refrigerant, and the power draw is limited because the compressor RPM is limited due to friction at internal seals or some other mechanical limit? This is the only practical reasoning I can find. However, I would find it surprising that the max refrigerant temperature is so much lower that it could affect power draw so drastically.
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