AC help needed. Is it leaking or need more gas?

[Bad_dude]

Hello everyone,
My car is a 1990 Honda Accord LX, 4AT. My AC is not working. It was working last week but not cold but cool enough so I left it. I bought this car as 2nd hand about 2 years ago. It's still in excellent condition. I did the AC diagnostic tests using the pressure switch and found out that the problem is lack of freon pressure.
I would like to know where do I go from here? I doubt that the previous owner ever refill the freon. So this leaves with 2 possibilities:
1) The system is leaking, thus not enough pressure for the AC to run.
2) The car is 20 years old and freon is never refill thus pressure drops with time.

I think it's more of the 2nd possibility but the first must be rule out first. So my questions are:
1) With the system using the old R12 freon, how can I can refill it? Or is it better to convert to the R134 system? If so, is it better or even worth it? How could I convert to the R134 system?
2) If it's indeed a leak, how do I know or test the system to find where the leak is? What is the most likely cause of the leak?

Thanks,

[James Matteu]

1a) With the system using the old R12 freon, how can I can refill it?
1b) Or is it better to convert to the R134 system?
1c) If so, is it better or even worth it?
1d) How could I convert to the R134 system?

2a) If it's indeed a leak, how do I know or test the system to find where the leak is?
2b) What is the most likely cause of the leak?

1a) You legally obtain R12 from a licensed technician, the tech will refill it for you.
1b) Yes, it is easier to convert to R134a.
1c) Yes, it is worth it.
1d) Replace the Low side connector and the High side gets an adapter cap. Once this is done, you can vacuum the system, add PAG, and recharge with R134a.

2a) Perform the conversion, recharge, then search for a leak with soapy water; bubbles means a gas leak is present.
2b) A dry O-ring or poorly seated Schrader valve. Both can be replaced for über-cheap.

[visualpoet]

Find and fix the leak before adding or changing the refrigerant. Have your local mechanic do it. They'll pump a small amount of UV dye into the system and then use a black light to locate any leaks.
If you're going to convert, have a licensed tech do it, they should pull the system into vacuum, make sure it holds (meaning no leaks) then charge the system with refrigerant. If they just vent it into the atmosphere, get your keys back and their information and call the EPA, there's usually a reward for turning them in.

[Bad_dude]

Of course I am going to have a certified mechanic do this job just b/c I know nothing about the AC system. I just want to learn enough so I won't get rip by the mechanic. How much do you guys think it would cost me to get this leak repaired if it is so, convert to R134, and recharged?

James Matteu, for the 2b answer, do you have a diagram or instructions on how this could be done?

Thanks.

[James Matteu]

No I do not. The o-rings are replaced with the lines removed and the valves unscrew with a "special" tool that comes with the replacement valves.

[accordluvr93]

make sure to check the pressure relief on the compressor. i had the same problem on my 93 ex. the a/c would leak out as fast as i could put it in, it was leaking from that valve being stuck open. you cant find replacement valves either so what i did was bought a bolt that fit in the hole and some washers then used the old o ring and put the washers on the bold to shorten it and hold the o ring in place. that cost me $0.15 and i have not had a problem with my a/c since