Why does my aircon drip into the foot wells (fiesta)?

Why does my aircon drip into the foot wells after I have used it for about 10 minutes on my fiesta?

Extra info - I recently changed the heater valve as the heater was not working (it's now stopped working again), could this have anything to do with it (does the aircon use the heater valve at all), or purely coincidence?

Many thanks!