MY19 Mazda CX5 Akera Diesel excessive generator voltage

Wide voltage fluctuation with ventilated seats turned on.
When voltage is low the seat ventilation stops working.
When voltage is high the seat ventilation works as expected.
Therefore as the voltage moves from low to high, the seat ventilation speed varies from non-existent to adequate.
The voltmeter turns off beyond 15V and resets when voltage drops below 15V. The workshop manual states that generator voltage must not exceed 15V.