Heater will work then blow cold air. I have to restart the car to have the heat work and still then blows cold

Hello, the first thing that needs to be determined is if you have a concern inside the car, or inside the engine compartment. If your engine is operating at the proper temperature, then you have a concern inside the car. Check first to ensure the inlet and outlet hoses of the heater core are both very hot -- use extreme caution checking this - you can get burned. If they are, then under the hood is OK. Inside the car, your climate control unit could have a concern, the temperature sensor, the temperature blend door actuator, or the door in the evaporator case itself could have a concern. Testing is needed to find out what is happening.