Heater not working properly, doesn't get as warm as it should, fan is working, appears that the control that regulates the flow of air is not working properly

Heater controls are not vacuum actuated on a 2001 Taurus. Heat is delivered to the cabin via an air blend door controlled by a servo actuated air blend door controller. There are dozens of reasons there is no heat but the most common causes are:
Air Blend Actuator is not functioning, because of blown heater fuse, broken power connection to blend actuator (org wire), open connection to control potentiometer, (temp knob) failed blend controller, stuck/seized air blend actuator lever, plugged input or output heater/coolant hose, plugged heater core, low coolant flow due to: low coolant level, reversed thermostat, corroded impellar vanes on water pump.

BTW, check thy problem in that order....
Oh...I should mention I have one of these beasts and I've been through this (that's why I'm here responding) and it turned out that some id10t that installed an aftermarket stereo broke the power connection to the air blend controller *and* pulled out two of the connetions from the temp selector knob (blend controller potentiometer).

Sound like a vacuum leak. you can check this by spraying wd40 very carefilly on the vacuum lines under the hood. the idle will change when a leak is detected. could also be a modulator valve or vacuum line under the dash. check this with a spray bottle filled with water. dont want the smell of wd40 in the cabin