Hear a clicking sound behind my radio

Sounds like the blend door is not operating. You need to check the vacuum pipes etc. Unfortunately the only way to do this is by strippng down the dashboard?

The temperature control switch:
is a potentiometer that outputs a variable voltage to the temperature blend door actuator to set the position of the temperature blend door.
Initiates closing of the heater control valve. When set to full COOL, a lever on the temperature blend door pivot shaft depresses the pintle of the heater control valve vacuum switch. The heater control valve vacuum switch then applies vacuum to the heater control valve, closing off engine coolant flow to the heater core.
Is serviced only with the climate control assembly.