Is Freeze 12 better than 134a?
 

The AC on my 1985 300CD only blows moderately cool after the shop evacuated/recharged with 134a. They didn't give me any further info, so I intend to get a manifold guage set & diagnose. If further work is to be done (replace compressor, drier/receiver, expansion valve), would it be beneficial to go with Freeze 12 instead of 134a?

if you do that extensive work, it's BEST to put True R12 back in.
Freeze 12 is a blend of chemicals that will put out cold a/c, but if there are ANY leaks, the system needs to be totally purged and recharged with correct amount again. one of the reasons it's called a "junk" refrigerant. also, the shops that will service your system are very limited, and correct fittings and labels are not often found.

Freeze 12 contains some R134a BUT genuine R12 is still available. In these older A/C systems nothing beats R12. The certification test in open to the public and less than $20 and you can do the entire thing online.

The marketers of Freeze 12 claim it's "more efficient" but the truth of the matter is it makes more pressure on the compressor discharge side (sometimes bad for old design systems.) "More efficient" doesn't automatically mean the air in the car will be cooler.

X2
Dupont spent a lot of time and $$ working out that R12 was the best. Problem was no one had any interest in ozone at that point in time.
If you can get R12, use it !! Its still the best.
Over here you cant get it any more, import ban & prohibition.
You guys are lucky.

If you are able go with R12 as stated above.

YOU DO HAVE AT LEAST ONE 'LEAK'... because your system is built with a designed leak at the front shaft of the compressor...to keep the front seal lubed... so every 4-7 years you need to top off a system typically ( assuming no other leaks).... but you can not top off a blend.. so another point in favor of R12...

My indy has put Freeze 12 in my unconverted '87 and it seems to work OK but genuine Freon-12 is still the best, if you can get it.