Where is the cabin air filter?

If your A/C isn't cooling check these things. With engine running hood up see if compressor is engaged when A/C is on. If not could be low on refrigerant.If it engages and disengages that means it's just a little low. If the above seems to be working properly you could have a damper door stuck. The way General Motors controls air temp is by adding warm air from the heater core. Hope this helps.