air conditioning

Look at your climate control module. conduct a self test on the system by doing the following: With the car off - turn on the key and shut the HVAC system off. Press the floor and off buttons at the same time and with in two seconds press the automatic button -- this puts the system in self test. If you get codes 24 or 25 or both, one of two issue are present. 1st replace the climate control module if that does not fix it replace the blend door actuator. This is a 5-6 hour job and the dash must be removed to complete.

I am not sure if your Mercury used blend air doors controlled with electric motors, cables or vacuum diaphragms to operate the heater control flaps behind the dash but they are not operating properly. If you are going to investigate it yourself there is a company that independent auto repair shops "buy" their information from that offer a very reasonable service to do it yourselvers. You can get a one week subscription or year subscription very cheap. The information is year make and model specific repair procedures, service bulletins, component locations, wiring diagrams ect.... great quality information same as the professionals have ,much better than generic workshop manuals from parts stores, much cheaper than the factory manual try http://bit.ly/mitchell_repair_manuals_online and get an online repair manual subscription.