Yes, R-134a refrigerant was commonly used in car air conditioning systems, including the 1991 Buick Park Avenue, after R-12 was phased out. So, if your 1991 Park Avenue's AC needs recharging, it will likely use R-134a. However, it's crucial to be sure, as some older systems might have been converted improperly or may still (though less likely) contain R-12. A qualified mechanic can properly identify the refrigerant type and safely recharge the system.
The coolant in the radiator is completely separate from the air conditioning system's refrigerant. They don't affect each other directly. The radiator coolant cools the engine, while the AC refrigerant cools the cabin air. However, a malfunctioning engine (due to a coolant issue) *could* indirectly affect the AC if it causes the belt to slip or the compressor to overheat, but that's not a direct interaction between the two fluids.
