Heater does not turn off

Do you mean the heater blower does not turn off or that you can turn the hot/cold to cold but still get hot air? The first could be a bad relay or switch that operates the blower motor. The second would likely be a failed blend door actuator. If you can clarify the question we can work on the problem together. Thank you.

Okay, that would be a blend door actuator issue. The air mix actuator is mounted on the bottom of the HVAC case to the right side of the foot well (item E in the second picture) and uses a short rod to connect to a plastic lever that moves the actual door. To see if the actuator or the lever is the problem you can watch the unit move (or not if it has failed) when you select hot/cold temperatures. If it does not move or if the plastic is broken or the transfer rod has failed it should be easy to see it. The plastic lever tends to crack and the shaft does not move when the actuator moves.