The best chemical for flushing any auto a/c system is a/c flush which can be purchased at your local auto parts retailer.....although it can be a little pricey. The second best solution is to use denatured alcohol which can be found almost anywhere--wal-mart,local drug store,etc..-a couple of quarts should do the job nicely.be sure to back-flush the system(reverse flow from normal refrigirant path)and make sure to use your compressed air and shop blow gun to force all of the flush and contaminants out of the system before reassembly.the flush should come out clear when clean.--oh yeah--don those safety glasses! hope that helps..