One time ac works, the next it doesn't

[SCOTTFISH]

Can anyone tell me why my 89 300se's ac works one time you start the car and the next it may not? I have had it checked for leaks, it has a new blower, and has be recently charged. Friday it only blew warm air. Saturday it was back in the shop that charged it before and it blew ice cold for over an hour and never did quit. Then, I took it to the grocery store and it worked fine until I came out to go home and then it blew only warm air. It sounds like to me like a loose connection. Larry Bible suggested that it may be something electrical and I can agree. Has anyone ever had this problem? Any suggestions?