Jburns is correct here, it's the whole system that needs replacing. In one way it's a good thing, newer systems are more efficient and work better. Toss in a smart thermostat and you can recoup you up front cost over time. If you get this fixed I suggest you get some estimates for new systems while this one is still going. Then you can weigh what to do, what SEER rating you want to pay for etc. Shed is painted, well mostly, ran out of paint. So after the rain I have to do the touch up and finish the trim. 97+ degrees and painting a shed was hell.