Is the engine warming up to operating temperature? Also, is the engine coolant clean and full? Either of those things can cause a heat issue as well as a partially clogged heater core.
First, pay attention to the engine temp and make sure it is at operating temperature. If it does, then the thermostat is good. If it doesn't warm up, replace the thermostat. Next, check the coolant level. If it is full, then I need you to try something. Start the engine and let it reach normal operating temperature while the heater is on high. When it is warm, feel both heater core hoses. Both should be hot. If that isn't the case, then the heater core will need flushed.
Please explain what you meant by you adjusted the cable for heat.
Here are a couple of links you may find helpful:
Let me know what you find or if you have other questions.
Take care and God Bless,
Tuesday, February 9th, 2021 AT 5:17 PM