Hello and welcome
The most likely problem (assuming you mean not blowing cold air from the a/c, rather than jammed on blowing hot air all the time!) is that the a/c system has lost pressure. There is a safety cut out in the system which means when the refrigerant leaks out and the system gets below a certain pressure, the magnetic clutch on the a/c compressor is disabled so that the compressor doesn't end up running "dry" and seizing up.
A refrigerant leak is by far the most common cause of a/c failure and is often missed in cool climates or in winter months.
The easy thing to do is to set the system to maximum cooling ("low" on both sides temp control, and a high fan speed) and check the a/c clutch to see if the middle of it is spinning, also you should hear a slight "clack" as it engages.