2003 Envoy AC Question

I am putting new front pads and rotors on my 03 Envoy this weekend and found some great info on the threads, I am going to use the Raybestos rotors(PG I believe) and Raybestos ceramic pads. I was thinking about semi-metallic until I read the threads.

I have an AC question I did not answered in any of the threads. It is an 2003 Envoy with rear air, I live in Arizona and we are quickly rolling into triple digit temps. If I park the Envoy outside and start it up the AC will not blow cool until I am driving, once I have been at speed for a mile or so it is blowing ice cold. I can start it and let it run for an extended period of time and it will not blow cold until I am moving. I have never had the system serviced and I am going to take it in for an AC Service but wanted to see if I could get some info/advice first.

Any advice is much appreciated.