well in my Carrier AC, the Auto starts on medium fan setting & eventually goes to Low & sometimes even lower then Low i feel when the room reaches its temperature of 25C. The intial Fan Speed depends what the ambient temp of the room is when the AC is turned on.With Auto, ive seen the fan speed is set at high and that is noisy tbh. Noisy not for sleeping, but maybe for the HT purpose. So i turn it down to medium setting.
Havent tried Auto for long periods of time and will have to check that.
Where do you live btw ? Im in Gujarat and the temperatures here easily touch 42-44 in Summer.
I m from Mumbai & man we had a super hot summer this time.
Cheers.