I have changed over a few of my Avanti s to r134 -you minimal have to change out receiver /dryer, o-rings completly flush system w/ cleaner to remove traces of old oil . Install new compressor w/ ester oil, charge to ~ 80% of r-12 capacity- better to go by weights. If you do not change all hoses to " barrier hose" you will have to top off ever 6-10 months as r-134 partical size is much smaller than r-12 and w higher r-134 static pressures will seep out through walls of hoses. 31 5w