My vent control stuck in defrost mode yesterday. After turning the control knob back and forth a bunch of times it finally started going into the other modes and sending air through the other vents. Today I put it back in defrost mode to see if it would come out again but it won't. If I turn the fan to low speed I can hear a faint clicking sound when I turn the knob in and out of defrost mode. Does anyone know what might be causing this?