Air conditioner when the air conditioner is on it only blows hot air

Check whether the warm air isn't going in with the cold air .Coolant line that runs into the firewall on the passenger side of the engine which is toward the bottom half of the firewall on the passenger side. If there is warm air going into the vents with the cold air then it blows warm air. You may have to shut it manually because it gets stuck sometime. Check it out.