Climate Control Servo
Yes, I think that is the case, that the servo is not allowing coolant to the heater core. As long as your switch is functioning, you can control on off at the dash. Remember, don't remove the servo or disconnect the electrical connections, as it plays some roll in your A/C function. This is a pretty easy fix. Clearance under the servo is a little tight when hooking the hoses to the copper line, but no big deal.