how do I add freon to a 2005 mercury mountaineer

They do not use freon any more. Now they use R134a.

You can do it yourself for about $30 or less.

http://id-usa.com/how_to_recharging.asp


Good Luck.

you should never add freon to a vehicle. always start with a/c system empty. it is best to vacuum the system first, but not necessary
check the sticker under the hood to see how much 134a the system holds [should be about 2lb.] and put the freon in the low side fitting[ it is narrower then the high side] with the engine running and the a/c on[the a/c system will suck it out of the can]