Originally Posted by Iamfink2

If I recall the owners manual states that the recirculate mode automatically turns on for 30 minutes when using the air conditioning whether you turn it on or not and you can't put on the fresh air til the 30 minutes has passed. If you turn on and off the recirculation button w/ac you will hear no sound difference in the fan but if you turn the ac button off and switch on and off the recirculation button you will hear a difference in the fan sound.