Hissing noise when I press AC button.

Definitely sounds like a problem with the air conditioning refrigeration system. It's normal to hear some gurgling and maybe hissing for a few seconds after you turn off the system. What you're hearing is the refrigerant boiling inside of the refrigeration system. That's normal. But since you are also hearing a clunk, when the compressor comes on, that's not normal. I'd suspect that the compressor is worn out and not pumping as efficiently as it should. You also hear the noises when the defroster is on because the refrigeration system for the air conditioning comes on to dehumidify the air being blown onto the windshield. This prevents the windshield from fogging over. I'd suggest having a pro check out the air conditioning refrigeration system. They will hook up gauges to the system and be able to determine what's going on. They can also leak check the system by pulling the system down into a vacuum and seeing if the vacuum holds. Hope that helps! Jim

but the initial noise i heard was the sound of a hose blowing or coming off... a pshhhh followed by some grinding like my brake pads were grinding on rotor but the next day it didnt make that noise again just the hissing when i turned on AC

I have a 2018 CRV that is making the exact same noise. I also noticed that the AC is not cooling down as it should. I was wondering if you resolved this problem. Mine goes in on Monday.

Hello, My 2019 CRV just went in for the same problem. It was a high pitched chime/whine that got worse over time. It would get really noticeable when the car was turned just shut off. They found that the Expansion Valve and O-Rings on the AC System.

GuruG8LN38 any update to this? Im the same situation same year model.