1997 Lincoln Town Car Question: Heater fan works fine but blows only cool air.

Heater core inlet & outlet hoses are same temp, hot. So core should not be stopped up, right? I can hear a clicking sound under the dash. As the blower blows cool air I asume the control doors are open correctly to let the air flow. Cannot find any lose vac. hoses. Eng temp is fine.Cannot locate the heater control val. is it elect or vac operated? Thanks