More than likely you have a blend door issue or another issue in the heater core. However the way this works is the air is routed over the heater core and when the coolant gets hot and is passing through the heater core, it heats the air that is coming into the cabin.
So if the heater doesn't work until it gets pretty hot then I suspect we have an issue with the blend door not routing the air completely over the heater core.
Here is a guide that will help with this:
https://www.2carpros.com/articles/car-heater-not-working
https://www.2carpros.com/articles/replace-blend-door-motor
The air should be getting hotter the hotter the engine gets so if it is cold and then all of a sudden it is hot then again, that is a blend door issue.
Please see the info attached below from the manual on how to replace this. Please let us know if you have other questions.
Thanks
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Wednesday, August 25th, 2021 AT 1:58 PM