If you have an imported car::
Check the air control lever in the heater controls
that selects Fresh or Recirculate. The indicator plate around this lever
normally has two positions indicated by arrows showing air entering the
car, or going in a circle. For defrosting it should be in the
position to bring in fresh air. This is probably the most common reason
people's Japanese defrosters do not work well, they have the air position
lever set to re-circulate. Recirculated air
holds moisture we breathe out, and it condenses on the windows.
For best defrosting
on an import: select Fresh Air, and turn on the Air Conditioning, with
the temperature lever to your desired comfort level. The air-conditioner
de-humidifies the air before heating it. Air Conditioning can help remove
humidity from the air. On many import cars there is a separate button to
turn on the Air Conditioning. With the control set to defrost,
you can turn on the A/C on days above freezing to remove humidity from
air and help remove frost of the windows. The air can still be heated by
adjusting the temperature lever to warm. The Air Conditioner switch is
separate on some imports, built in to the heat / ac / defrost lever on
most domestic cars.
U.S. model cars: Most U.S.
cars bring in fresh air and turn on the air conditioning when defrost is
selected.
Other Possibilities: One other possibility for defrost problems is a leaking heater core. You might also notice the smell of anti-freeze if this is the case. Replacing a heater core in some cars is a major job, and beyond the scope of AutoTips. Also check for low engine temperature, an air-conditioner not working, and proper operation of the air doors that select the air. If your heater is not working well, there are other possibilities on the AutoTips Heater Tips page.