I have a 1991 Corvette that has nothing displaying on the AC controller except for --- :( . I have replaced the controller itself but get the same results. I thought it could the temperature sensor unit in the car however I have not idea on where it might be located.

My 1990 has been doing this for a number of years. It does it when you start the car. I found that when it happens I can cut the engine off and restart it and usually it corrects itself. Sometimes it takes a couple or three starts before the temperature will show on the display instead of the three dashes. The first time this happened I left work in July and it was about 100 degrees (central South Carolina) and the thing was locked on heat and it was blowing full blast out of the floor outlets. I was scared to cut the car off since I didn't know what was wrong and the control function was locked. That was the most miserable 15 mile drive I have ever made.

Hello
Under the hood in the top of the a/c housing on the pass side firewall the fan control unit mite be bad, it gets very hot and the plug will melt. If it fails nothing will work.
David