Just because it's made by Toyota!
Toyota's engine is too weak.
Most small taxi(Xia Li) in China, don't open AC at all in hot summers, the driver don't dare do so.
I bet it's a Tercel or Corolla or I4 Camry, can not be anything else.
and if you dive with AC on , you will find you use more gas than driving a full size car.
heavy duty makes the engine works out of it's normal range.