1. Check the Obvious First:
* Coolant Level: Low coolant means your engine isn't getting hot enough to provide heat to the heater core. Check the coolant reservoir and add coolant if necessary (use the correct 50/50 mix of coolant and distilled water). If the level is consistently low, you have a leak somewhere in the cooling system – this needs immediate attention.
* Temperature Gauge: Is your engine actually getting up to operating temperature? If the gauge stays low, you have a problem with the thermostat, cooling system, or possibly the engine itself.
* Fan Speed: Is the blower motor fan working? Try different fan speeds. If it's not working at all, the blower motor, resistor, or fuse/relay could be faulty.
* Heat/AC Controls: Make sure the controls are set to "heat," and the temperature is turned up high.
2. Common Heater Problems and Solutions:
* Faulty Heater Core: This is a common failure point. The heater core is a small radiator inside the vehicle that transfers heat from the coolant to the air blown into the cabin. Symptoms include lukewarm air or no heat, even with a hot engine, and potentially coolant leaks inside the vehicle (sweet smell, wet carpets). Repair: Replacing the heater core is a major job requiring significant disassembly of the dashboard. This is best left to a professional mechanic unless you have experience with automotive repair.
* Blending Door Problems: The blending door system controls the mix of hot and cold air. A malfunctioning blending door can prevent hot air from reaching the vents, even if the heater core is working correctly. Repair: This can be a moderately challenging repair. Often involves removing parts of the dashboard to access the blending door mechanism, possibly requiring replacement of the actuators or linkages.
* Thermostat: A stuck-closed thermostat will prevent coolant from circulating properly, resulting in poor heating. Repair: Replacing the thermostat is a relatively easy repair, but it does require draining some coolant.
* Water Pump: A faulty water pump won't circulate coolant effectively, leading to poor heating. Repair: Replacing the water pump is a more involved job than replacing a thermostat.
* Blower Motor Resistor: This controls the fan speeds. A faulty resistor can cause some or all fan speeds to fail. Repair: The resistor is usually located under the dashboard and is relatively easy to access and replace.
* Blower Motor: A failed blower motor will prevent any air from flowing through the vents. Repair: Accessing and replacing the blower motor can vary in difficulty depending on the vehicle model but is generally considered a moderately easy repair.
* Fuses and Relays: Check the fuses and relays related to the heater and blower motor. A blown fuse or faulty relay can prevent the system from working. Repair: Relatively simple repair, just locate and replace the faulty component.
3. Diagnostics:
* Feel the Heater Hoses: With the engine running and at operating temperature, feel the two heater hoses going into the firewall. They should both be hot. If one is cold, there's a blockage or problem in the cooling system (perhaps a clogged heater core).
* Visual Inspection: Look for any obvious leaks around the heater core or hoses.
Recommendation:
Unless you're comfortable with automotive repair and have the necessary tools, it's best to take your 1998 Chevy Blazer to a qualified mechanic for diagnosis and repair, especially if you suspect a heater core or blending door issue. These repairs can be complex and time-consuming. A proper diagnosis will save you time and money in the long run.
