98 Outback dash controls climate control system

I have a 98 Outback that has the push buttons to control or direct the air flow of the heat/air conditioning. Sometimes the buttons don't work as they should. They push in/out just fine but the lights don't illuminate and the air flow doesn't change vents to the appropriate place. Other times the lights work fine and the air changes as it should, no problem. Any ideas on why this might be happening? Thanks, Drew