If the coolant level is low, the thermostat may not be able to open properly, which will prevent hot coolant from circulating through the heater core. Open the hood of the vehicle and locate the coolant reservoir. If the level is below the "MIN" mark, add coolant until it reaches the "MAX" mark.
Check the Heater Control Valve
The heater control valve is a valve that controls the flow of hot coolant through the heater core. If the valve is stuck closed, hot coolant will not flow through the heater core and the car will not produce any hot air. Locate the heater control valve, which is usually located near the firewall. If the valve is stuck closed, you may be able to free it up by gently tapping it with a hammer. If the valve is still stuck closed, you may need to replace it.
Check the Blend Door Actuator
The blend door actuator is a motor that controls the position of the blend door, which mixes hot and cold air to control the temperature of the air that comes out of the vents. If the blend door actuator is not working properly, the blend door may be stuck in the closed position, which will prevent hot air from flowing into the cabin of the vehicle. Locate the blend door actuator, which is usually located under the dashboard. If the actuator is not working properly, you may need to replace it.
