Is it a new or an old window unit? Assuming your looking to refill it I will assume it is an old window unit which most likely uses R-22 refrigerant. R-22 is an ozone depleting refrigerant that is being phased out but should be available until 2010. There should be a label on the window unit stating which refrigerant is used.
134a refrigerant.
An Air Conditioner needs the Type of "Refrigerant" that is stated on the (Identi-Plate) usually located near the condenser.
r134a
R134a
134A freon
The A/C uses R-134A refrigerant.
A 1998 Jeep uses R134a.
134a is the refrigerant used by most vehicles made after 1995
If it's later than 99 should be 134A
If it's under eaves. if not you might consider some kind of cover so can use in inclement weather.
Most home systems use R-22 refrigerant. R-410a, known as PURON, is also an increasingly used refrigerant. If you see a pink sticker on the outdoor unit, it will say on the tag with the model and serial numbers r22 or 410a. "Freon" is a trademark of DuPont, and is NOT the real name of refrigerant. "Freon" was R12 and is no longer made.
There is a misconception that all refrigerants are freon. The EPA has band use of freon R12 in the USA. It is no longer produced stateside. The only refrigerant that is acceptable for automotive use is R134A. If you are to attempt to service your air conditioner you will need to know the exact amount needed. It is very critical on cars.