A blockage in the heater core. When your vehicle’s engine has cooled down, open the radiator cap and check the level of coolant. Tragically Pets Die Every Summer Because They Are Left In Cars Cars Heat Up Very Quickly Winding The Window In 2020 Summer Safety Tips Heat Exhaustion In Dogs Dogs Why is my car heater not working? Why is my heat not working in my car . Learn how to check your coolant level here. Air in the coolant system. If the coolant level is low, the core isn’t working, or there’s air in the system, your car’s heater may. Either the blower isn't working, in which case you may get warm air but not much of it, or it is blowing air but it may not be very hot. If the coolant level is low If cold air is coming out of the heating vents even when the vehicle is warmed up and the thermostat is set to hot, you could be dealing with one of the following problems: You start it up and hit the heater. Because we rely on the coolant system to provide us with ...