* The Blower Motor: This is the fan that pushes air through the system. If it doesn't work, you'll get no air, regardless of the settings. Check the fuse first, then the motor itself. It might be seized or have a bad connection.
* The Heater Core: This heats the air. If it's clogged or leaking, you'll have weak or no heat. This is a more involved repair, often requiring some disassembly of the dashboard.
* The Defroster Vents: These direct the air to the windshield. Check for obstructions (like debris) blocking the vents. Sometimes the vents themselves can become stuck or broken.
* The Blend Door: This is a component that controls the mix of hot and cold air. If it's malfunctioning, you might get only cold air, even with the heat turned up. This is also typically a more involved repair requiring dashboard work.
* The Vacuum System (Possibly): Some 80s cars use vacuum lines to control the vents and blend doors. A leak in the vacuum system can cause the defroster to malfunction. Inspect the vacuum lines for cracks or disconnections.
* The Temperature Control: A faulty temperature control unit can prevent hot air from reaching the defroster vents.
Troubleshooting Steps:
1. Check the fuses: Start with the simplest. Consult your owner's manual to locate the fuses for the blower motor and heater.
2. Test the blower motor: Turn the fan speed to high. If you hear nothing, the motor might be bad. If you hear a weak sound, there could be a problem with power or the motor itself.
3. Check the heater: Ensure the temperature control is set to hot. If you have heat elsewhere (floor vents), the problem might be with the defroster vents themselves. If you have *no* heat anywhere, the heater core is likely the culprit.
4. Inspect the vents: Check if the vents are blocked or if they're physically able to direct air to the windshield.
5. Listen for vacuum leaks (if applicable): While the engine is running, listen near the vacuum lines for hissing sounds.
6. Check the coolant level: Low coolant can affect the heating system's performance.
If you've checked these and the defroster still isn't working, you'll likely need a more in-depth inspection and possibly professional repair. A mechanic familiar with older vehicles will be best equipped to diagnose the issue. Remember safety first – be cautious when working with any automotive systems, especially those involving coolant.
