Have a 2000 Honda Accord 4 cylinder. Problem started last week. Turned a/c to cold, cold air not as cold as before, plus a loud hissing sound that seems to be coming from the passenger side, under the glove compartment. So, turned a/c off, and just use air vents (turned off the recycle air button). Hissing sound continues, and cold air comes out of whenever car is in motion, colder than having a/c on. Is the car in big trouble? I have smog check due soon too...Anyone knows what is happening or has experienced this situation?
It sounds to me like you probably have a so-called "vacuum" leak. The "hiss" you mentioned is a tell-tale sign, and your air conditioning mode controls (both hot/cold, duct selection, etc.) are controlled by vacuum lines under the hood. At least, everything I just said it true of my Chevy Blazer, so I assume your Honda could have similar engineering. Sometimes these are easy fixes---especially if you look around where you hear the hissing and see a little hose the width of a pencil disconnected, or perhaps really deteriorated.
These aren't exactly your car---but they're diagnosing similar symptoms.
(This one isn't as similar as you might think, as it amounted to a bad compressor, I don't think your problem is as dire.)