98 Firebird A/C blows low air - not very cool

let me know if this is right, the a/c was working fine at first on high 3/4 then you lost cold air, Was it still blowing out air {hot or cold}? When it started to put out cold air again you turned it up and heard a noise under the hood. but it worked all right on 1 or 2.
When you raised the hood where was the air sound comming from? When it is hot and humid out and you shut the a/c off you will have a sizzling sound at times. it is from the cold evaporator warming up to the outside temp.
Start the car up with the hood open, turn the a/c on listen for any leaks and listen to the a/c compressor. After a few minutes shut the cars a/c off and listen , let me know what you hearn and find.

thanks for you response, first off let me explain again the problem in more detai:

-using AC on level 1 - it was too cold so i turned cold knob to less cold
-then it got a lot muggier and i turned the cold knob back down to coldest setting- a little bit later i noticed little cold air coming out of the vents so i turned it up to level 2 - still lil air coming out though it was cold
-when i turned it to level 3 and 4 is when i noticed the noise coming from under the hood (loud and almost grinding, but not quite - a grinding whirring noise = )
-when i turned the car off i popped the hood and heard the hissing noise

-i did what you recommended and this time cold air DID come out from the vents at all levels - even with high blast at levels 3 and 4
-there was STILL a hissing air sound near the compressor (uhh pretty sure i know where this is located = ) when i turned the AC off BUT i couldnt tell where it was coming from and everywhere i put my hand i couldnt feel the "air"

i thought it best to check the fuses but how do you "check" them? should i just replace them? and if so, do i replace the all the AC related fuses? the fuse thing confuses me

--funny thing is i JUST got my drivers window fixed caused it was off the channel and wobbling and now my AC is on the fritz, the irony!!--

let me know your thoughts - id hate to pay for a diagnostic if i can do it myself!

Trying to figure out what is happening.
answer a couple of questions for me please.
1. does cold air come out when turned on?
2. Does the cold air blow out when you turn the fan on? 3. when you turn the fan control up does the air blow out more? The hissing sound could be from the evaporator. The grinding sound can you tell where that comes from?

yesterday after leaving work, everything worked fine but it made noise (imo, right where the fan/blower is) at levels 3 and 4 so i only used it at level 2 and everything was fine

yes, cold air now comes out and it no longer seems "obstructed" meaning it comes out normally, not at a lower rate

after more thought on the matter, i wonder if a leaf or twigs got sucked into my fan and it only makes noise when it is on a higher speed cause of this "blockage"? -- i feel like i should check out the fan to make sure nothing is stuck in there, whadya think?

That could be the problem or the fan motor should be checked. Its a tight space to remove the fan , Once you have the motor out vacuum the inside of the housing to clear any other obstructions that could be in there Let me know what you find out