can r12 be replaced by r409a?

I have a 91 Buick Park Avenue and want to recharge the A/C. It is becoming very hard to get R12 overhere, one shop recommends the r409a refrigerant.
Is this a good substitute?

Buy convershion fittings for 134A at any local Autoparts store, and buy 134a from Big lots for $8.00 a can.

I found a shop who offers 2 other substitutes for R12: R413 and R437a.
R437a is a new refrigerant. Is it better as a substitute than 413 and 409?

I'm not familiar with what is the common refrigerant used in new vehicles over there. In the U.S., R-134a is what is used. It is a pure gas, tetrafluoroethane. Because it is pure, it is currently recyclable by professional shops and because it does not harm the ozone (so they say), can be handled by the average guy as well. However, shops use equipment that can remove and store it on site, to keep it from entering the atmosphere.

All of the refrigerants you mention, R-409, R-413, R-437, etc., are actually blends of different pure gases to try to mimic the performance of an old refrigerant without causing as much damage to the ozone should it be released. Using one of those would require someone experienced in handling that refrigerant in particular.

As mentioned, there are many R-134a retrofit kits available in the U.S., but please let us know what is used over there.

My recommendation would be to convert over to what is used in new vehicles over there, which should be the R-134a. The big reason being is that should your car's A/C ever need service, the refrigerant can be recovered without requiring the shop to dispose of it as a hazardous substance, which can be costly. Using the -409, -413, or -437, you would be beholden to that shop to do all your future work.

Hope this helps!

R134a is the standard refrigerant over here as well. Converting is too costly and time consuming.
I've found a shop where recharging is not expensive. R409a doesn't seem to be suited for automotive a/c's. R437a seems to be the best alternative for R12.

Do what you want, but how is R134 more expensive??? The fittings are $6 and the refrigerant will cost you about $20.

You are probably getting quotes for a whole system conversion which is the "right" way to do it, but if you flush the system and recharge with PAG oil and r134 it will cool the car. Expect average vent temps to rise about 2-4 degrees, but you can expect that with any "incorrect" refrigerant.

I've done several r134 cheapo conversions and they work fine.