- Low coolant level: If the coolant level in your car is too low, it won't be able to circulate properly through the heater core and warm up the air that is blown into the cabin. Check the coolant level and add more if necessary.
- Faulty thermostat: The thermostat in your car controls the flow of coolant to the heater core. If the thermostat is stuck open, it will allow too much coolant to flow to the heater core, which can cause the air that is blown into the cabin to be too cold. Check the thermostat and replace it if necessary.
- Blocked heater core: The heater core is a small radiator that is located behind the dashboard. It heats up the air that is blown into the cabin. If the heater core is blocked, it won't be able to transfer heat to the air, which can cause the air that is blown into the cabin to be too cold. Check the heater core for blockages and clean it if necessary.
- Faulty blend door: The blend door controls the flow of air from the heater core and the outside air. If the blend door is stuck open, it will allow too much outside air to mix with the heated air from the heater core, which can cause the air that is blown into the cabin to be too cold. Check the blend door and replace it if necessary.
If you have checked all of these things and the heater still blows cold air when you slow down, you may need to take your car to a mechanic for further diagnosis.
