1991 Cadillac Brougham airconditioning not functioning properly

had not been driven in a few years... the compressor was not working, but could get the heating/defrost to work while in ecno mode. replaced the compressor, filled refrigerant, start car press auto set temp @65 blows out air until you start driving then only blows air out at your feet, doesn't feel cold but is cool...can hear the compressor cycling on and off and is making a humming noise. also after you stop the car and place in park the air again blows out of the front vents....do you know why this is doing that....if you switch it to econo only get outside air that blows thru vents???