how can you get 230 degrees on convection?

Are you sure that you realy need to get to 230° (°C or °F?) in convection mode?

Around 200° when the convection forced circulation fan is working will heat about as fast as around 400° in purely passive conventional mode.

By the way, are you sure it's a "microwave" oven? Hybrid microwave-convection ovens are extremely rare...

Electro
July 2013