1990 Geo Prizm air conditioner

I dont think this was the problem but maybe. Well I was driving on the freeway and I shifted the transmission to 2nd gear and the car got very loud so I shifted back to drive and as soon as I shifted to second my air went to very hot. So I took it to midas and they said I had freon in it and they claimed it was the control switch so I went to the junk yard and have gotten 3 of them and the air still doesnt work. Before I took the car to midas u could press the ac button and the light and fan would come on but after they touched it, it never worked again so could someone pleasetry and help me and the heater works like a champ at all times