'93 Buick Riviera AC Problem

I've had my Riv in the shop off and on for the past two months with an AC problem. The climate control goes over to "economy" mode instead of "auto". We replaced the low pressure switch, and it ran for a week then cut out again. When the mechanic clears the codes on the computer it will run non-stop at the garage, but when I go about 10 miles it cuts out again. I also have a problem with the digital dashboard cutting out--could these problems be related? Any ideas?