Why Is the Car Defroster Only Blowing Cold Air?

If the defroster is unable to blow hot air, there may be a clog in the cooling system or a malfunction of one of the actuators for the vent doors. The cooling system and actuators will need to be properly inspected to find the source of the issue.

A defroster produces heat using a heater core, which uses coolant to heat the air for a vehicle. Hoses run coolant into the heater core, which warms the air and sends it through the vents. There are several components in the climate control system that can malfunction and cause it to clog. When this occurs, the thermostat, heater core and radiator should be promptly inspected.

The actuators are special flaps that control the flow of air in the climate control system. When these doors are stuck shut, the heated air will not be able to reach the cabin of the vehicle. The following instructions explain how to troubleshoot the actuators.

  1. Locate the actuators
  2. The placement of the actuators vary on the vehicle and are generally located behind the dashboard. The dashboard may need to be removed.

  3. Test the actuator
  4. Some actuators use air vacuums to function, while other use a cable. Test the door to see whether or not it opens and closes.

  5. Replace the actuator
  6. An actuator cannot be rebuilt, and if a part is malfunctioning, then the unit must be replaced.

  7. Test the actuator
  8. Reinstall each part previously removed and test the new actuator.