Airconditioner keeps freezing over...?

My duplexes airconditioner stopped working. I had it to 65 cause it was hot. THe duplex had someone come out and fix it and the person told me that I cannot have the airconditioner lower then 73 degrees or it will freeze again and that no airconditioners are meant to go under 73 ever. I have it on 73 now and it has been over an hour and it is 78 degrees inside the duplex now. It only bought it down a few degrees. First is it true that 65 degrees is to low for any airconditioner or do they just not want to fix the problem. It is very very hot in here with myself and my 3 children.