if the system is still pressurized with refridgerant, you should be able to tell by checking system pressure (compressor off) R12 and R134a have different pressures depending on temperature. At 70F, it's way too close to call. At 40F or 100F, you should see a difference. But you'll need a refridgerant detector to know if they have been mixed, or god knows what else put in there.

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.