1. Coolant Level and Condition:
* Check the coolant level: Low coolant means the heater core isn't getting enough fluid to heat. Check the coolant reservoir (often a translucent tank). If low, add 50/50 mix of coolant and distilled water (NEVER just water). A severely low level could indicate a leak, requiring professional attention.
* Check the coolant condition: Is the coolant rusty or sludgy? This indicates corrosion and possible blockage in the heater core or cooling system. Flushing the cooling system might be necessary.
2. Heater Core:
* Clogged heater core: Over time, the heater core (a small radiator inside the car's dashboard) can become clogged with debris or rust, restricting coolant flow and reducing heat output. This often requires replacement, a fairly involved job.
* Leaking heater core: A leak will cause a loss of coolant and possibly a musty smell inside the car (from the coolant leaking onto the carpet). Again, this usually necessitates replacement.
3. Blend Door Actuator:
* Malfunctioning blend door actuator: This small motor controls the amount of hot and cold air mixed. A faulty actuator can prevent hot air from reaching the vents, even if the coolant is hot. This is often a relatively easy repair (though access can be tricky).
4. Thermostat:
* Stuck thermostat: A thermostat that's stuck closed prevents coolant from circulating properly, resulting in poor heating. This is usually a simple and relatively inexpensive repair.
5. Blower Motor and Fan:
* Blower motor: A weak or failing blower motor won't move much air, regardless of the temperature. Listen for unusual noises or weak airflow. Replacing the blower motor is relatively straightforward, but access may be challenging.
* Blower motor resistor: This controls the fan speeds. A faulty resistor might limit the fan to only one speed or prevent it from working at all.
6. Vacuum Lines:
* Leaking vacuum lines: Some heater controls rely on vacuum lines. Leaks can affect the heater's operation.
Troubleshooting Steps:
1. Start with the easy checks: Coolant level and condition, and checking the blower motor speed and fan operation.
2. Listen for noises: Unusual noises from the heater system might point to a specific problem.
3. Feel the heater hoses: With the engine running and the heater on, feel the hoses leading to and from the heater core. If one is significantly cooler than the other, there's likely a blockage or problem with the heater core.
4. Check fuses and relays: Check the fuses and relays related to the heater system (your owner's manual will show the locations and ratings).
5. Consult a repair manual: A repair manual specific to your 1999 Dodge Intrepid will provide detailed diagrams and instructions.
If you're not comfortable working on your car yourself, it's best to take it to a qualified mechanic for diagnosis and repair. The cost of repair can vary greatly depending on the problem. A simple thermostat replacement is much cheaper than a heater core replacement.
