Rep Power: 0

I have a 03 Civic Si ep3. I don't know if it's the A/C compressor, Blower of something else. Air is not cold at a sitting idle, when going the air will be really cold, but after a while it will just be air, and back to really cold later, almost like it had it on thermostat lol.. any help would be appreciated.

 
Rep Power: 517

Sounds like you need to start with making some observations while the system has stopped cooling.

Open the hood and check:
Are the radiator fans still running?
Is the compressor clutch engaged?

 
Rep Power: 132

Maybe the A/C clutch and coil clearance needs to be adjusted (i.e. closer together). This was my issue when I had a fading out A/C after a couple of minutes of driving. Dealer recommended a new clutch and coil!

 
Rep Power: 0

Yes the radiator fans are still running, compressor clutch in engaged. Still does it. Once I get down the road going it will start cooling. If stopped at a red light or traffic it will not cool.

 
Rep Power: 0

Yes the radiator fans are still running, compressor clutch in engaged. Still does it. Once I get down the road going it will start cooling. If stopped at a red light or traffic it will not cool.

 
Rep Power: 517

Are you the OP of this thread? Lose your login, made new user ID?
How about...
Engine idling = poor AC cooling
Engine RPM raised = better AC cooling?

I'll guess probably low refrigerant, needs system inspected to see if a specific leakage point can be found and fixed, and refill/recharge.