Air passage switching system for air conditioner

An air passage switching system comprising:

• a case for forming an air passage through which air flows;
• a door disposed rotatably in said case, for opening and closing said air passage, said door including
• a door body,
• a rotation shaft for rotating said door body, said rotation shaft having first and second ends in a longitudinal direction of said rotation shaft and disposed at a center portion of said door body, and
• a seal member made of an elastic material and attached to said door body;
• and
• a link member connected to said first end of said rotation shaft, for rotating said rotation shaft;
• wherein:
• said door body has a first cylindrical portion disposed concentrically with said rotation shaft at an outer peripheral side of said first end so that a circular hole opened toward said case is defined by said first cylindrical portion;
• and
• said case has a second cylindrical portion extending toward said door, wherein:
• said second cylindrical portion of said case is inserted into said circular hole in such a manner that a gap is formed between an outer peripheral surface of said second cylindrical portion and an inner peripheral surface of said first cylindrical portion in a radius direction of said rotation shaft while said first cylindrical portion and said second cylindrical portion are overlapped in said longitudinal direction by a predetermined length.