What would cause AC to blow warm air one day and cold air the next day?

Hello, I feel for you, because you just bought this car and it has a phantom issue that you are needing to resolve. Intermittent air conditioning concerns are both a blessing and a curse. On one, hand, if the system develops cold air at some point, you know that there isn't an active leak, and that your compressor works. On the other hand, it's a mystery as to why you get cold sometimes, and warm others. Your compressor coil or clutch could be intermittently failing. Your cycle switch could be a concern. Your temperature controls inside the vehicle could be at fault. Hands on testing to see how the system under the hood is working at the time you have warm air is essential.