Q: When turning the temp. selector from cold all the way to hot, does it click?

Hello. The problem sounds like a blend door actuator motor. It controls where the fresh air is drawn in from when the switch is moved. There are actually two different areas that can supply the air, depending on whether you want hot or cold. When you move the switch to the middle for warm air, the air is drawn from both sources at the same time, and therefore gives you air that isn’t fully hot or fully cold.

Anyway, when the blend door actuator fails, it doesn’t have the ability to move the door to the correct position. It will see a command to be in one position and keeps trying until it is in the correct position. When it can’t move, it just keeps trying, hence the clicking until you switch it back to the other position. If you would like to verify the problem, a qualified professional from YourMechanic can diagnose the clicking sound and assist with any needed repairs.