In order to remain compatible you should use the same type of freon that is in the system already. If the system has not been converted to R134a it would have R12 in it. R12 is much less used now and more expensive than R134a. You might want to consider having it converted to R134a
If it has been converted to use R134a then use that freon.
You should have this verified but the freon is probably HFC134.
Was built for R12, should be converted to R134a
Was built for R12, should be converted to R134a
It was built with R12, but should be converted to R134a.
R-134A
R134a
R134a
R134a
R134a
R134a
R134a
R134a