No heat blend door is working

Hello,

Make sure the coolant level is correct as low coolant can trigger no heat out of the heater due low circulation of coolant through the heater core.

If the thermostat fails at stuck open position, it will not allow the engine to warm up enough, which will impact the heater performance and blow cool air.

Here is a helpful guide on the typical causes for no heat:

https://www.2carpros.com/articles/car-heater-not-working

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.