A/C button does not light up?

Hello,

Just to clarify, the blower fan only comes on when you turn the knob to #4, right?
It is likely a blower motor resistor that causing this.
Over time the pins on the resistor can get burned out and make the fan to only work on one speed.
The blower motor resistor is located on the side of the blower motor. It can be accessed by removing the glove box.

Here is a helpful video of how to do this:

https://youtu.be/IoAdY2twhFI

https://www.2carpros.com/articles/blower-fan-motor-works-on-high-speed-only

You mentioned when you push the A/C button it does not light up. Does the A/C work as it's supposed to when you press the button?
If it works then the light might be just burned out inside the switch.

I have attached the blower motor resistor diagram for your reference.

Please let me know of any questions.

Thank you.