The old refrigerant is commonly referred to as R-22 or Freon. The new refrigerant is called Puron by Carrier and R-410A by Trane. Puron/R-410A works exactly as R-22 does but does not contain the chlorine that supposedly can destroy our ozone layer. Puron/R401-A uses a different type of oil and runs 50% higher pressures with the same temperatures as Freon. This is why you need to change the refrigerant piping, evaporator coil and the metering device when converting from the old to the new. The cost per pound of Puron/R410A is slightly higher than that of Freon but as Freon is phased out you can expect that to change in 2011.