I have an intermittent hissing sound (like steam from a radiator) whenever fan is on. Will last a few minutes, then go away for a few minutes. Only using heater this time of year, so it's not AC. Besides, had entire AC system replaced last year. Turn fan off, and hissing goes away, never had a bad fan hiss before, if that's to blame.

 

Do u have it on defrost when it makes that sound?

 

Yes, it's set on split, defrost and vent. So I must be hearing defrost cycling. Is that hissing normal then on a 2006 Touring w/ (new) rear AC?

 

that hissing sound is then the freon moving through w the defrost on the ac compressor comes for for a short time to remove moisture from the incoming air.
If it gets worse then u have low freon and a leak some where.

 

Thanks Kevin, hope it's not a leak & she blows cold for our B'more summer!

 

the hissing is the freon passing through the evap core in the dash.

 

Can this also be the issue on my truck, getting same noise, same location and shortly after I turn on heat/defrost. It does stop especially after I have been driving it and it gets warm. I thought it may have something to do with moisture, I was just guessing. Thanks!