Amazon product ASIN B0002JMEQWView: https://www.amazon.com/FJC-2710-System-Flush-Kit/dp/B0002JMEQW
The first thing you'll need is something like that. Here's the great news: You don't have to buy one. Autozone and others have it in their loaner tools program. It's real simple to operate, it'll either have a fitting for your air hose from your compressor or a schrader valve. Fill it up with the appropriate solvent, either connect the hose, or air it up via the valve. After that it's simply a matter of holding the business end up to your various hoses and fittings and blowing the solvent through. Just don't flush the receiver/drier (in fact,
REPLACE IT!) and make sure you pull the orifice tube prior to the flush (
AND REPLACE IT TOO!!!).
Now, when it comes to which solvent to use, there are a lot of choices. I've personally used this one a lot:
https://shop.advanceautoparts.com/p/ac-pro-certified-a-c-pro-flush-clean-solvent-based-1-quart-cqs-11/7060432-P?searchTerm=a/c flush and had good results every time. Make sure you get a name brand, either from a refrigerant manufacturer or an a/c parts manufacturer (such as this one from Four Seasons, which is a leading aftermarket A/C system supplier:
Amazon product ASIN B004AEQSE4View: https://www.amazon.com/Four-Seasons-69994-Super-Solvent/dp/B004AEQSE4/ref=sr_1_16?dchild=1&keywords=cqs-11+a%2Fc+flush&qid=1592698070&sr=8-16
), as there are a lot of no-name products out there on the internet, and only they know what they're putting in them.
If you don't have access to a compressor, a few of these cans is a good alternative:
Amazon product ASIN B004BSHVUYView: https://www.amazon.com/dp/B004BSHVUY/ref=dp_cerb_2
I've used them in a pinch, and they work well enough, just not quite as good as using a flush can with pour-in solvent.
Two important things to remember when you're done with flushing the condenser, evaporator, and hoses/lines:
1. Make sure and keep blowing air through the parts of the system well after the solvent and/or debris has stopped flowing to make sure there is no solvent or debris left behind.
2. Fill the system with the correct amount of A/C system oil when putting it all together. You will want to use
ESTER oil, not pag or mineral on an older car that formerly had R12. The reasons for this are twofold; the ester oil is compatible with any remaining mineral oil left in the system, and ester oil doesn't chemically react to any R12 residue that might linger somewhere in there.