I just redid the A/C on my Challenger, Evaporator & Condenser I flushed, if you have a air compressor Auto Zone has the flushing tool in their loaner program... Free!! Score!! They also loan a Vacuum Pump... Anyway, the way I went about it since I didn't want a mess in my engine compartment, I hooked a #10 fitting up to the suction size of the evaporator, & a #6 to the fitting where the expansion valve connects, & attach a 3-4' length of hose to each.. Don't try to force it all the way on it'll be coming apart anyway... So now you need the flushing tool & flushing solvent... Flushing solvent used to consist of R141 which used to be cheap, I just checked online & now it's $160 a gallon.. I passed..
For the past few years I've used Denatured Alcohol... It does a decent job, as long as the system isn't full of metal it works fine... If the system is full of metal you need to replace the Evaporator & condenser, period... Anyway, a gallon is $14 & it'll do two systems pretty throughly.. So, free flushing tool, cheap flush solvent a few fittings, direct the waste solvent into a bucket.. Flush away... When your done flushing blow compressed air through the system for 15-20 minutes to evaporate the alcohol & put the system in a vacuum to boil off anything that might remain... The open the system, inject oil in the components, reassemble & vacuum again for 1/2 hour & charge it up...