My daily driven Geo Prism's A/C worked fine until about week ago. its been chilly due to weather, so i didn't use A/C at all. Its gotten bit worm today, so I turned A/C on only to find out no cold air. I've checked obvious, like make sure temp knob is in right spot, or knob is stuck in heat. Which knob works, as i turn it to hot, air does get hot. I've also checked to see if compressor is comming on, which is does. I can hear clutch kick on and off with A/C switch. i can also see the foaming is going on when compressor is on through inspection window on accumulater, which suggest me that there are R123 in system. So i'm bit dumb founded. what else should I check?