Jim the 'fridgerant I used is called EcoFreeze EF22A it was a special deal we had a few years back this was one cyl left over I thought might as well use it up..it works great. SUPPOSED to be compatible with all R22 systems, we've used it quite a bit (4 cyls worth) and with no problems. I can get all the 22 we need so probably just go back to 22 in the old package systems we have here. We get in a lot of surplus military HVAC units,most were 22 based and are evacuated before they sell them so we recharge them before resale.