Most HVAC control units suffer a dim or not visible display. This problem is caused by some surface mount resistors in the back of the unit. A few minutes with a soldering iron and this can be fixed for free.
Need procedure for dash panel/console removal added here.
Here is the backside of the HVAC unit. Remove the four screws.

Leaving the unit face down lift the back off the face. The face contains many buttons and parts that will fall on the floor if you seperate it or invert the face while it is off the back.
Looking at the back now, remove these four screws.

Wiggle the back circuit board out of the plastic housing. Set it down with the pins facing up.

These five surface mounted resistors are the issue. They need to have the solder reheated to reflow it.

This is done by touching a soldering iron to the metal ends of the resistors

Reassemble the unit and go try it out. It should work again.