Yes they work, and may buy you another season. With R22 this year retail at around $30+ per pound, and going higher, and availbility next year in question.....you may seriously consider why you would spend much money on a 20 year old, probably 8 SEER system. You would probably cut your electric bill in half with a new 13~15 SEER system, not to mention that your 5 ton unit is probably over-sized. Your system probably takes 7 pounds of R22. You can not ever replace your indoor unit, as the SEER mismatch would be very difficult to set up.