Okay, I'm at wits end...2000 Grand Marquis that I love, except:

My a/c blows warm, and after some research I checked that my a/c clutch is engaging and the line in the engine compartment to the (accumulator tank?) gets COLD telling me my freon is good...so I started looking into the blend motor door/actuator, since that's very common issue I understand.

Since I didn't want to remove my entire Panel and pull the dash back, etc...I pulled my Glove box, and cut a small viewing "hatch" into the plenum chamber to view the blend door operation. I can see the blend door and it operates fine. When I put the control on "Max Air" it swings one way, when I put the control on "Floor" (heat) it swings the other...indicating the door is being actuated, and is operational.

What the heck do I look at next?

 

Just an idea - try to squeeze the hose that feeds hot water to the heater (squeeze the hose with a C clamp, using two laundry clips to avoid puncturing the hose) , and see if the blown air gets any colder without the heat source.

My guess would be that the A/C may need to be checked with a gauge connected on the low pressure port. I had a similar problem where the pipes in the engine compartment were getting cold but there was no true A/C inside.

HTH ...