i have a 2001 Grand Marquis and the A/C worked great yeasterday and now it just blows very hot air /as if the heater is on???

Your temperature blend door is stuck in the heat position. Either the blend door itself failed or the actuator failed (usually it's the actuator). It's possible to replace the actuator without ripping the dash off completely, but it does need to be loosened. The passenger air bag will have to removed as well. Reach in through the air bag opening you can view/feel the actuator, which is a flat square white plastic box sitting on top of the AC/Heater plenum box (which holds the heater core and AC evap coil). You won't be able to reach all the screws as the back screw is too far under the dash, but loosen the ones you can reach. Snap the actuator off leaving the back screw in place. Buy a new actuator and in the rear screw hole (the one belonging to the screw you can't reach) cut a slot to the hole in the flange. This will let you slide the actuator into place with the screw in place. Then place the other 3 screws and tighten. You can connect the wiring harness before placing the actuator and adjust the temp and see it moves before installing it as a test. Go to Crownvic.net forums as they have a detailed write up on how to replace an actuator without removing the dash, just use the search terms "replace actuator." I've had to do this several times as I tend to buy/fix police cruisers and this happens frequently. Will take a novice about 3-4 hours, but once you've done it about 45 min. Hope this helps.