Car defroster problems should be dealt with quickly, as defrosters that are not working properly can make winter driving difficult and even dangerous. Fortunately, car defroster systems are not complicated, so it's easy to diagnose problems.
Car defrosters use heat from the engine's coolant to warm the air. The coolant runs through and warms a radiator-like device called the heater core. A lack of heat from the defroster is often due to a low engine coolant level, though the problem may also be a clogged heater core.
Air is moved from the heater core into the passenger cabin via a series of ducts. The direction of air within the ducts is controlled in most vehicles by vacuum-powered doors. Broken or unhooked vacuum hoses often cause the doors to stop working, resulting in loss of air direction control. A clogged cabin air filter may also reduce the flow of air.
When a blower fails, the first thing to check is the fuse. The owner's manual for the vehicle lists the location of the fuse box as well as the position of the blower fuse in the box. If the fuse is good, a voltmeter should be used to make certain the blower is receiving power and is grounded.
