If the coolant level is low, it can cause the heater to blow cold air. Check the coolant reservoir, which is usually located under the hood of the vehicle, and add coolant if necessary.
2. Check the thermostat.
The thermostat is a device that regulates the flow of coolant to the heater core. If the thermostat is stuck open, it can cause the heater to blow cold air. To check the thermostat, start the engine and let it warm up. Once the engine is warm, feel the upper and lower radiator hoses. If the upper hose is hot and the lower hose is cold, it may be a sign that the thermostat is stuck open.
3. Check the heater core.
The heater core is a small radiator-like device that is located behind the dashboard. If the heater core is clogged, it can cause the heater to blow cold air. To check the heater core, turn the heater on high and feel the air coming out of the vents. If the air is cold, it may indicate a clogged heater core.
4. Check the blower motor.
The blower motor is the device that blows the air through the vents. If the blower motor is not working, it will not be able to blow the heater air into the cabin of the vehicle. To check the blower motor, turn the heater on high and listen for the sound of the fan. If you can't hear the blower, it may be faulty.
If you have checked all of these things and the heater still blows cold air, it is possible that there is a fault in the heater control unit or the wiring.
In this case, you should consult a qualified mechanic for further assistance.
