Climate control lights flashing- heater always on just a little, and cant turn it off, or AC on.

With the engine running do you have vacuum to the vacuum control switch in the heater control?

The display is backlit and you most likely need to remove it and have it repaired as the bulb is hard wired to the circuit board

Have a good mechanic to check to see if the door of the a/c and heater and defroster is working properly. I had the same problem and one mechanic said he could fix it for $750. I got it fixed by an honest mechanic for less than $100. Good Luck!!

The heater/AC control is fairly complex. AC is used to defrost windows even in the winter, so not unusual to have it on. Is this a climate control system with temperature sensors or just manually controlled from dials on the heater control? Could be just the heater control is bad. If a climate control system, then we need to look at all of the sensors first.

You should make sure you have proper charge for sure.has your battery gone dead lately? I know on some of them digital climate controls will act exactly like this and have to be reset or go through a setup sequence.

If it is a digital control modual they were known to go bad.

Could be a number of things, usually a blinking screen indicates that the climate control module is defective. But not always, If one of the vent doors jammed of a solenoid for one of the doors malfunctioned It would cause the screen to flash.

Your Climate control unit may have to be reset. The reset works as follows: With the key in the ignition and in posistion 2 push both the defrost button and the recirc button (at the same time) for five seconds or untill the led lights in those buttons begin to flash. Wait for 30 seconds or untill the led's stop flashing. Switch off the ignition. Check the evaporator temp sensor and pressure sensor for correct functionality.
Courtesy of benzworld.org/forums

U must remove the climate control unit from the dash and remove the top cover of the unit, u will find a tiny twist in light bulb socket with a tiny little light bulb, this provides the backlight for the AC/heater display, u can buy the bulb at any auto parts store, couple of bucks.