Mercury Repair Questions? Ask a Mechanic for Answers ASAP
Hello David and thank you for your question,The common cause for the type of problem you are having is in most cases cause by a failing blend door actuator . The blend door actuator control the air coming through the AC evaporator and heater core . That being said I would test it to be sure before replacing any parts to be sure the signal is getting to it from the control panel. I have enclosed the test steps in the link below for the testing as well as replacement.https://dl.dropboxusercontent.com/u/104923897/Blend%20test%20Jul%206.pdfhttps://dl.dropboxusercontent.com/u/104923897/Blend%20door%20EXP%20%20Jul%206.pdf
The blend door actuator is the common cause but in some cases it can also be a problem with the door its self. If in fact the actuator is at fault your looking at about $85 for a new actuator and right at 2 hours to remove and replace it. That being said , I would have them do the testing to be sure and that will usually run you about another hour in labor. The dealer is a little pricier but in the long run have plenty of experience with this type of problem and would be my first choice to make this repair.