Volvo C30 No Heat
 

2007 C30 2.4i. Last night was driving home when suddenly my heat quit working. Coolant is full and the hoses going to and from my heater core are both warm, meaning the core is not clogged. The climate control unit can still switch between vents, but when I turn the dial to adjust the temperature nothing happens. I can hear the servos moving in the dash, but there is a light tapping sound associated with this movement. Any insight would be greatly appreciated. I have read this can be a damper motor or linkage going bad. What is the best way to diagnose this?

First, look at the damper motor and its parts. Check them for any damage or wear. Also, check the wires and connections.
Check the blend door actuator for problems or blockages.
Next, make sure the control valve works well and lets the coolant flow freely.
And see if there are any error codes for the climate control system.