If you have the climate control set to Auto, it will take a few minutes before the fan gets going. You can override it by turning the splitter knob to 'MAX' and turn the fan speed setting from 'AUTO' to 4. 'MAX' setting should put the fan on maximum speed anyway, so turning the fan speed knob is probably not necessary. That will give you maximum defrost setting on cold mornings.
That said, it doesn't do a hell of a lot until the engine starts warming up. Make sure the aircon is a) on, and b) works(!) as the dehumidified air speeds up demisting a lot.
Btw, 4 bars here, solid as a rock. I've only ever seen the 5th bar once and that was on a really hot day, stuck in traffic.