[230kACCORD]

I have a hissing sound from under where the HVAC, every since we bought the car back in 1999 my parents say it has always been like that but never this loud, so ima try my best: it goes hisssss, then it goes away, then hissss, the sound come and goes. I was thinking a expansion valve, and I don't have leaks.

 

[teezythakidd]

I'd say that's normal... most "older" air conditioning units do that. Even conventional air conditioner units. I think its a pressurization thing with the freon that produces the noise.