Heat control in my 04 P71

Ok....the other night, it was finally cold enough to use my heater. Normally I have the a/c on. Turn the temp knob, and still ice cold!. Jump ahead, a day. Now, temp is hot, and I can't turn the temp down! The a/c parts, under hood, are ice cold, so I know the unit is working, but wondering if a simple replacement of the unit, behind the knob, might cure my issue??? Any ideas, people? Thank you for your time!

UPDATE~!!!!!!!!!!!!!!!!!!!!! I have now replaced the unit, behind the temp dial, on the temp control panel. NO CHANGE! Now I have a new part, that I did not need! Any suggestions where to go from here?? I seem to recall a fix, for something of this nature, having to do with the blend doors?? (If thats right!) The temp is up on high heat, and turning the temp knob does nothing! The control for where the air goes...ie.....the defrost vents, floor, mix, vents, etc., is putting the air in the right location. Fan speed goes up and down. But still NO temp control!!
HELP! lol!

check the heater box resistor under the hood.

more likely than not the actuator motor is acting up. located under the dash. resistor problem is when fan only blows on high. resistor is fan. actuator is heat output. had heater in my 07 only blowing warm not hot. changed thermostat. flushed heater core. problem was actuator motor. dash must be removed. these cars should bake you with fan off and set on vent. temperature gage set all the way to the extreme right. mine have manual knobs not electronic. chicago is cold and these cars produce a tremendos amount of heat. about a four hour labor charge. 60 dollar part from ford. i only use ford parts not cheaper stuff from auto zone.

New to the forum here, Gang...........................I think I have a "blend door" actuator problem, vehicle is a 2000 Mercury Marquis, that has a loud "clicking " noise when you crank up the car.

It's behind the dash, and usually goes about 10 cycles, before it quiets down.
Naturally, now I have no fan flow, nor fan control, but the heat can still be routed, (somewhat!), to the defroster, or the floor.

When you speak of dash removal, sounds to be a MAJOR job!!!....................................Is it?

Is it something you would attempt, ( I'm a mechanic, by trade, on aircraft), or would you hire it out???

Dealing with the airbag(s)............Something a person could handle, as long as the proper precautions are followed???

Where could a fella' find some guidance, on this procedure, and are there any "shortcuts", as in going in through a removed glovebox cavity, or the like, to do this procedure????

Thanks in advance, for any help you could offer on the subject!!!

It would be nice to have a good defroster again!



Chuck