1. Check AC fuses. Check your owner's manual to find out which fuses control your vehicle's defroster. If any of these fuses have blown, replace them.
2. Check vacuum lines. If your vehicle's defroster relies on vacuum lines to operate, check the vacuum lines under the hood and in the dashboard for leaks or damage. Repair any leaks or replace any damaged lines.
3. Check actuator/blend door. The actuator or blend door may not be working properly. Inspect the actuator and blend door for damage and replace if needed.
4. Check heater box. The heater core may be clogged or damaged, preventing hot air from reaching the defroster vents. Flush or replace heater core.
5. Check blower motor resistor. The blower motor resistor may not be working properly, which can prevent the blower motor from blowing hot air through the defroster vents. Test the blower motor resistor and replace if needed.
