95 grand marquis

Yesterday I turned on my a/c and it blew cold. Today I turned it on and it blew hot air and I popped the hood and checked the compressor was working fine. But the "refrigerant tank" excuse me I don't know the name of the black cylinder beside the coolant tank. But it was freezin cold somebody please help me thanx.

Seems like the ac system is working correctly, almost seems to me that the door inside your "duct work" under your dash that separates your heater core "heater" from ur evaporator "a/c" (maybe called condenser, I forget) isn't working properly. Possibly run on a vacuum controled selector. Old cars were run by a stiff cable/wire, u know, where u had to slide it between cold and hot, but I'm sure its run by vacuum on a 95. Anyway, I would look under the dash on passenger side and see if I could see such an item, maybe drop glove compartment open to give better access? Does it blow as hot when the engine temp is low and gradually get warmer as temp increases? If so that's where I'd go is to the vacuum control to that door

Blend door, its called a blend door (just popped into me head) and the vacuum control is called an actuator......... I think