You don't have to take the compressor off to convert the system. You can suck all the old stuff out, run a flush, and then use the new stuff. You have to replace the accumulator, the orifice tube, and the fittings...if you want it a little colder squeeze the orifice aperture down a smidge. Take out the compressor...no...back when retrofits first started happening that's what they told us we had to do...but nope! One word of caution though...if your compressor is original, if it is just the teeniest bit noisy, opt for a new one...R134A is a thicker freon...it will tax a weak compressor. Just another note...a compressor job here would set you back $650.00.