1. Low coolant level: If the coolant level is low, the heater core will not be able to circulate hot coolant and will therefore blow cold air. Check the coolant level in the overflow tank and add more if necessary.
2. Faulty heater control valve: The heater control valve is responsible for regulating the flow of hot coolant to the heater core. If the valve is faulty, it may not be allowing enough hot coolant to flow through the core, resulting in cold air blowing from the vents. Check the heater control valve for any signs of damage or leaks and replace it if necessary.
3. Clogged heater core: The heater core is a small radiator located behind the dashboard that transfers heat from the engine coolant to the air that flows through the vents. If the heater core is clogged with debris, it will not be able to transfer heat effectively and will result in cold air blowing from the vents. Flush the heater core with a garden hose to remove any debris and restore proper airflow.
4. Faulty blend door: The blend door is a flap that controls the mix of hot and cold air that is blown through the vents. If the blend door is faulty, it may not be opening properly to allow hot air to flow through the vents. Check the blend door for any signs of damage or obstructions and replace it if necessary.
If you are unable to identify and fix the problem yourself, it is best to take your vehicle to a qualified mechanic for further diagnosis and repair.
