Hyundai Getz fans not coming on

When the engine is started in the morning the ventilation fans do not come on to clear the windscreen - even when they are turned up to full - after the engine has warmed up (guage half way) they still don't work and then later on in the journey they just start randomly. Can anyone help why this is as it means that the screen takes ages to clear. The air is set to airflow from outside but changing that or the air outlet location (Feet, face, windshield) doesn't start it.