If you replace an older A/C compressor (approx 12-15 yrs old), do you have to replace the heating unit ?

Our A/C compressor is leaking freon and needs additional freon...not sure if you can put additional freon in the old compressor because of the new laws--the unit does take R22? If we have to replace the compressor (which is outside) do we have to replace the heating unit in our attic...the heating unit was replace about 5-7 years ago.