Get your A/C serviced. Shouldn't cost more than RM70 (RM55 at my place).
If anything is wrong, it should be spotted by the mechanic during this process.

Just make sure the A/C shop you go to isn't a cut-throat

If...
--> car move = cold air, car idle = warm air; there's a compressor leak (compressor kong )

--> car move = warm air, car idle = warm air; there's either no more gas or gas leak somewhere

--> erratic hot/cold cycles; either valve or electronic problem


Talking from experience (very expensive ones apparently )