Ac was running cold one day then the next day it wouldn't cool the car down

Hello, Check your fuses first when there is an issue with any sort of electrical component. If your fuses are good and the compressor is running, you might have a small obstruction in the unit, the interior or exterior temperature sensor may be failing, or a host of other issues are possible. Since there are very few items in an air conditioning system (refrigerant system) that can be serviced at home, I always recommend just to have it connected to a set of gauges to see what the system is doing.