If you meant to ask why your heater isn't blowing hot air (or is blowing cold air, or lukewarm air), then the problem could be several things:
* Low Coolant: The most common cause. Check your coolant level in the radiator overflow reservoir. If it's low, you have a leak somewhere in the cooling system. Adding coolant is a temporary fix; you need to find and repair the leak.
* Thermostat Stuck Closed: The thermostat regulates coolant flow. If it's stuck closed, the coolant won't circulate properly, preventing the heater core from getting hot.
* Heater Core Problems: The heater core is a small radiator inside the car that warms the air. It could be clogged, leaking (resulting in a sweet smell inside the car), or simply failing.
* Blend Door Actuator: This controls the mix of hot and cold air. A malfunctioning blend door actuator could be stuck on cold, even if the engine is hot.
* Water Pump: The water pump circulates the coolant. A faulty water pump won't circulate coolant effectively, preventing heat from reaching the heater core.
* Clogged Heater Hoses: Hoses that carry coolant to the heater core could be blocked by debris or corrosion.
* Air Bubbles in the Cooling System: Air trapped in the system can prevent proper coolant flow.
To diagnose the problem, start with the simplest checks:
1. Check the coolant level.
2. Check the engine temperature gauge. Is it reaching normal operating temperature? If not, there's a problem preventing the engine from heating up properly.
3. Feel the heater hoses. Are they both hot? If one is cold and the other hot, there's likely a blockage.
If you're not comfortable working on your car yourself, take it to a qualified mechanic for diagnosis and repair. They have the tools and expertise to pinpoint the exact issue.
