2001 Nissan Maxima - A/C & Steering shake seems to be pr

I bought 2001 nissan maxima 2 months back. Never used A/C so far, when I was using A/c last 2 weeks back. I don;t see A/c is working very well, just normal comes out. But heater work very well. Any thought what needs to be checked?

Also, when I drive in Down and apply brake steering shakes little?

Any suggestions would be greatly appreciated

Thanks,
Prabhu