How can you tell if an older car has R-12 or R-134 in it?

You can't reliably tell what refrigerant an older car uses just by looking at it. There's no external marking that consistently indicates R-12 vs. R-134a.

The only definitive way to know is to:

* Check the sticker on the underside of the hood: Some cars *may* have a sticker specifying the refrigerant type, but this is not guaranteed, especially on older vehicles where the sticker may be faded, missing, or illegible.

* Check the service records: If you have complete service history for the vehicle, it might specify when and with what refrigerant the AC system was serviced or recharged.

* Have a qualified mechanic check it: A professional automotive technician with the proper equipment can determine the refrigerant type through a variety of methods, including pressure testing and analysis of a sample of the refrigerant itself. This is the safest and most reliable method.

Do not attempt to guess or test it yourself. Refrigerant identification should be left to trained professionals due to safety concerns related to handling refrigerants.