Renault Espace blows hot on the left and cold on the right!?

My Renault Espace blows hot air on the left and cold air on the right! The right side does sometimes get warm when I have it on full. The left side works fine all the time. I am looking for clues on what to do. I had thought of flushing out the cooling system thinking that there may be a blockage in the pipes and this may clear it. The cooling system did have a leak 18 months ago and this was resolved. Not sure if that is related. Model is Grand Espace 2.0 Privilege Auto.

OFT
October 2010