There are a few reasons why the heater might not work. It can be due to the engine not warming up properly due to stuck open thermostat. Also, it could be due to a faulty blend door actuator that is stuck on the cold setting.
Take a look at this guide, see if you might have overlooked something:
The blend door actuator controls the hot/cold air flow or mix. It can fail and get stuck in either hot or cold position. If it is stuck in the cold position the heat will not function.
I have attached diagrams for your reference.
Please let me know if you have any questions.
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Sunday, January 9th, 2022 AT 3:12 PM