My car will blow cold air at first and then after a few mins blow hot air.

The a/c compressor can have a rpm sensor telling computer that is is working so computer will increase rpm of eng to increase a little at idle position. if clutch on compressor is getting hot the clutch will disengage and because it is getting a on signal but the rpm signal from compressor is 0, the a/c buttton will flash to let you know there is a failure. I would check the clutch for a 12v and ground signal and if there the magnetic clutch has fail. Usually a new A/c compressor would need to be installed. I hope that helped.