My 1988 Mera needs some R12. Last time I drove it the A/C seemed to be OK. It sat for a month or more and now it cycles on and off and does seem to cool but only slightly. I have a bottle of R12 I bought years ago knowing that it would be hard to get latter on. It is the typical large bottle used by service shops. I am wondering if I bought the hose and gauge kit if I could add to my 88 to bring it back to spec's. My friend did a total vac and refill several (5-6) years ago so I think my system is OK. It just needs a fill up. My fear is over filling it. I have a friend that is well versed in this and can do it for me. I am just wondering if I should attempt it?

I am far from an expert on AC systems, but I did something similar with my 19K mile '88 GT last year before I sold it. The difference is I brought it to a shop and had them add the R12 (about a pound). Since you have a friend with some experience then I say go for it.....if it were just you attempting it for the first time then I would say forget it.....at that point it would be worth teh $$ to bring it to a shop. I believe I paid about $250 for a pressure test and the refill of R12. Not cheap, but it was well worth it to me!

I say go for it!

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If your friend is well versed, it should be ok.
I don't have my R12 charts anymore, but look up the pressure for R12 to get a temp of about 35°F - 40°F.

http://www.ackits.com/index.cfm?fuseaction=Chart
This chart suggests 35 - 40 psi on the low side (the side you'll be adding refrigerant to).
So, purchase a set of manifold gauges and just add refrigerant until the pressure is between 35 - 40 psi. Lower pressure will give colder air, but if it leaks much at all you lose your cooling. I'd shoot for right in the middle and call it good.