Just because it's blowing warm air does not necessarily mean that it is low on freon. The climate control pushbutton unit can fail and allow the heater control valve to flow, which will make it blow HOT air, not warm, but HOT. This valve is near the battery, with heater hoses going in and out. A simple check would be to use a clamp on the hose to STOP the flow of coolant to see if this is the problem. If the clamp brings back cold air you really need a pushbutton unit, and if you replace it MAKE SURE YOU CHECK THE AUXILLIARY PUMP FOR CURRENT DRAW. If the auxilliary pump is drawing more than 1.3 amps, it will blow the new pushbutton unit.
This gives you something to check without spending money.