If you receive a cool air breath instead of warm air when you turn on your car’s heating system, it’s likely that something went wrong inside or around the heater core.
The latter is a small radiator that generates heat, allowing the engine cooling fluid to circulate through, so that the fan can enter the heated air in the passenger compartment to keep everyone warm. Since the heater core is usually placed in an uncomfortable position (behind the dashboard) you might look elsewhere before excluding the simplest possibilities.
First, check the coolant level when the engine is cold. If it is really low, you may not be able to heat the heater center. The cooling system thermostat may also be faulty, preventing the refrigerant from circulating. In these cases, there is a good chance that the engine will be warmer than normal, and there is a risk of overheating with costly consequences.
If none of these is the cause, the heater core and the auxiliary components are likely guilty. If water does not circulate through the heater core, perhaps a diverter or valve does not open to allow the flow, or the core itself has a loss or is clogged. Another possibility is that a door or diverter that should direct hot air inward is blocked.
On machines with automatic temperature control, the “set and forget” function should keep a constant temperature, but the computer that controls the system may be faulty. Then the heater core and other parts may work well, but the computer tired of satisfying your air conditioning needs and stopping working.
Since diagnosis and resolution of this type of problem can be complex, most drivers are probably looking for a professional opinion. If you are researching on the internet, however, there are many cases where there are DIY lovers who have faced this type of problem, but the heating of some of them still blows cold air.