Heater is not working?

Hello,

It sounds like you could have a faulty blend door actuator.
When you move the control from hot to cold or cold to hot, it controls a air door operated by the actuator. That actuator can go bad and stuck in one position. When this happens, you will not be able to switch from cold to hot or hot to cold.
The blend door actuator is located behind the dash. You will have to remove the radio to access it.

Here is a helpful article:

https://www.2carpros.com/articles/replace-blend-door-motor

I have attached diagrams for your reference.

Please let me know of any questions.
Thank you.