First off make sure you have the correct actuator, see this TSB. If you replace make sure you get the right one.
This TSB article is being republished in its entirety to remove reference to the 1998 Town Car.
Vehicles which are equipped with manual and Electronic Automatic Temperature Control (EATC) use different actuators. The actuators are marked "MAN" for manual and "EATC" or "ATC" for EATC systems. These markings are found on the part number sticker on the actuator.
1998 actuators differ from 1997 actuators on some vehicles (Crown Victoria/Grand Marquis, Continental, Explorer/Mountaineer) and are not interchangeable. Installation of the wrong actuator can cause potentiometer failure on manual systems, and no temperature control for both manual and EATC systems, as well as Diagnostic Trouble Code (DTC) 24 or 25 on EATC systems.
Refer to the Actuator Chart to determine if the correct actuator is installed into the vehicle and service as required.
This should help. Let me know.