1997 Mercury Marquis V8 Two Wheel Drive Automatic 112000 miles
My 1997 Grand Marquis only blows hot air on any setting. I have replaced the Blend Door Actuator and the Vent door moves freely. The electronic control appears to work but the blend door does not move.
I have the same car and had this problem after replacing "air door actuator" that had a stripped nylon gear. This appears to be a common failure and can be diagnosed by hearing a clicking sound from under the dash panel before it fails completely. Result is no movement of blend door by actuator, which means the air is mixed at whatever position the vent door happens to move to or be stuck in.
Mechanic who replaced the broken actuator did not realize that the EATC control module must be reset to re-synchronize the new actuator with the position of the blend door. This is done by running the self-test diagnostic. Procedure and details are copied below: 1) Pre-Self Test Procedure: All Automatic Temperature Control Modules
Before starting self test, the vehicle must be stabilized between 4.4 and 32.2 C (40 and 90 F).
Keeping the temperature within this range will avoid false Diagnostic Trouble Codes (DTCs).
2)Car off, close doors, start car w/EATC off.
3)To enter self test, simultaneously press the "OFF" and "FLOOR" buttons, then release and within 2 seconds press the "AUTO" button. All segments will light up if self test completes with no failures. Takes about 2 minutes.
4)To exit the self test and save all trouble codes, press the blue "COOL" button. To exit the self test and clear all trouble codes, press the "DEF" button.
NOTE: AFTER WORK HAS BEEN COMPLETED ON THE CLIMATE CONTROL SYSTEM, THE SELF TEST SHOULD BE RE-RUN AND EXITED BY PRESSING THE "DEF" BUTTON. THIS WILL ENSURE THAT ANY CODES ACCIDENTALLY SET DURING REPAIR ARE CLEARED.
I see that it has taken 2 years for a response to this question. Hope this helps someone else and future questions posted to this site are answered _much_ quicker.