I'm with you, definitely not blower motor. Blower motor controls the different fan levels and those do not affect the breathing sound.

Mine also started after having a leaking evaporator core replaced, so that's an interesting note.

I've been told several times that it means my compressor is failing or about to fail, but happily, that does not seem to be the case at all. The whole system has survived 4.5 Georgia summers since that evaporator core replacement, knock on wood.

I'm leaning toward the expansion valve explanation that I've seen in this thread, but I'm no expert.

And now I see A70BoosTFienD replaced his expansion valve and no change. So I'm actually leaning towards ignoring it as long as it keeps cooling.

Glad I found this post. Same issue. Once in 10-15 seconds the AC makes a sort of exhaling sound. New AC compressor, new evaporator.

I test drove a white 05 in Virginia that did this after evaporator install. Must use oem parts or this will happen. Been there with other vehicles.

Bump this up again
Obviously not an isolated problem

Try finding aircon servicing on this listing website.

I have an 05 and ordered an evaporator core when my mechanic said that was the issue. I have a great mechanic. Can fix anything on a car. Cost for labor was quoted at $300. We shall see. Big job I'm told.

Denso 476-0040 A/C Evaporator Core

Any update?

Just noticed it this evening while waiting outside a publix for the family.
I dont too much about the trucks history so I dont know whats been changed. Mine happens when the compressor engages as well then I hear a faint hiss/whistle. Like my truck is telling someone to come hither lol.

Was freaking me out for a sec because I just dropped a good dime on the friggen head gasket. I pray for a long life for this AC while my wallet recuperates.

Mine has done this since I got it about a year ago. I'm convinced it's the sound of the freon passing through the expansion valve into the evaporator core. I have a real simple fix for it though: turn up the radio. But seriously, as common as this seems to be I'm gonna treat it like it's normal. It's not hurting anything and the A/C blows plenty cold so I just ignore it.

I have the same problem in my 2003 4runner. I did replace the blower motor as it stopped working but the sound remains. The AC however, doesn’t seem to blow as strong as it did before. Don’t know what that means, Just sharing.

It's been about 7 years since I posted this thread. My 4Runner still makes the noise, but it seems less noticeable than it used to be. I don't think it's just that I've learned to ignore it.

The original compressor (that a couple of mechanics suggested replacing because of this noise) is still going strong after 225k+ total miles and 17 years of Georgia summers.

I am long past worrying about the noise at this point. It's just part of the truck, which I still love.