Heater blows either hot or cold, but not warm

Good morning,

I suspect a blend door motor failure. It is going one end to the other with no in-between.

It is under the dash left side of the heater case.

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

Roy

Hi,

It could be a vacuum leak, Check the vacuum line under the hood where it goes into the passengers compartment for vacuum. If the vacuum source is good, Check the vacuum at the actuator under the dash. If the vacuum is good check the actuator with a hand held vacuum pump. I'm attaching schematics and repair guides below. let us know if this was helpful or If you need more information.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Thank you,
Joe T.