r134
R134-a
It came from the factory with R12 Freon. Due to the high cost of R12, I suggest you convert it over to R134. Any good A/C shop can do this. Remember, it is illegal to release refrigerant into the atmosphere. It is also illegal to add refrigerant to a system with a leak without first repairing the leak.
Unless it has been converted to R134, the OEM refrigerant installed in 1991 was R12 Freon. I suggest you have it converted to R134 if it has not already been done.
Originally R-12 Should be converted to R134
R134 _ Well Mine did
R134 (Source: '94 Accord Manual)
It came from the factory with R12. Unless it has already been converted which you will know by a sticker placed somewhere on the system, I would most definitely have it repaired and then converter over to R134. R12 is just too expensive to consider using.
r134
what will replace R 134 refrigerant
it depends on the actual model Nissan pickup, but most vehicles made after 1994 take R134 refrigerant. The refrigerant type and amount is listed in the owner's manual.
R134