What I plan to do is change the expansion valve, condenser and dryer/accumulator myself and then bring the car to an A/C tech and have him clean the system, check for leaks and then recharge.
After reading the FAQs and some other posts I have some questions:
1. Do I need the FCP Groton $25 retrofit kit with the fittings and O-rings to do this properly? (I bought the above parts separately.)
2. Do I need to replace any hoses, or should I wait until the tech checks it for leaks?
3. Should I install some kind of a filter? (I read on a post that this could be important to keep the system clean)
4. I know I have to replace/change the oil in the compressor. Will I have to pull the unit to change the oil? It’s a 1990 with the original compressor. Do I need to put oil (Epson?) in any other components besides the compressor?
5. Do I need to “flush” the system prior to changing out these parts? Or can I just change them and then bring it to the A/C tech?
6. It appears that the $25 retrofit kit has a gazillion O-rings. Will it be obvious which rings to use where, and do the fittings on all the components I plan to change and/or extract require new O-rings. I notice the rings are color coded??

I know some of these questions are elementary in the world of A/C automotive repair, so thanks for humoring me, and thanks for your help.