What type of freon is used in a 1994 Ford Thunderbird?

first look for a label or sticker on the cross member above the radiator or on the compressor that indicates the amount of charge and refrigerant type (r-12 or r-134a). it's quite possible that the car was manufactured using r-12 and was retrofitted for r-134a since r-12 is no longer available. in any event, look at the schrader valve in the line near the compressor. it looks something like a tire valve and may have a cap on it and will be on the larger of the two lines going to the compressor. if it is the same size as a tire valve it is r-12, if it is larger it is r-134a. in any event if you need to add freon you will have to convert to r-134a since r-12 is no longer available. you can do this yourself with conversion kits available at any auto parts store. be sure to follow the directions. you don,t necessarily have to pump down the system doing it yourself but be sure to change the accumulator and oriface tube. most of the old oil is in the accumulator and this gets rid of it. the new oil for r-134a is different and will not mix with the old oil. make sure the retrofit kit comes with oil. if you can't get to the oriface tube leave the old one in at somewhat reduced efficiency. the whole job should be well under $100. alternately you can have it done by a mechanic but he will have to find out where the old freon went and look for a leak. hope this helps.