1. Identify the Problem:
* No heat at all: This points to a problem with the heater core, coolant level, thermostat, water pump, or a blend door actuator issue (rarely a complete failure on its own).
* Heat only on high: This often suggests a problem with the blower motor resistor or the blower motor itself.
* Heat only on certain settings (e.g., only hot or only cold): This usually means a faulty blend door actuator (controls the mix of hot and cold air) or a malfunctioning blend door cable (less common on this year).
* Uneven heat distribution (hot on one side, cold on the other): This could also indicate a blend door or actuator problem, potentially a blocked duct or a faulty air distribution flap.
* Blower motor works, but no air: Could be a vacuum leak in the system controlling the air flow.
2. Troubleshooting Steps:
* Coolant Level: Check the coolant level in the radiator and overflow tank. Low coolant will significantly reduce or eliminate heat. Add coolant if necessary (use a 50/50 mix of coolant and distilled water).
* Thermostat: A faulty thermostat that doesn't open properly will prevent the engine from reaching operating temperature, resulting in little to no heat. A relatively easy replacement if needed.
* Water Pump: A failing water pump won't circulate coolant effectively, leading to poor heating. This is more involved to replace.
* Heater Core: A clogged or leaking heater core requires replacement, a fairly involved job. Look for coolant leaks under the dash (a telltale sign).
* Blower Motor Resistor: This is a common culprit for heat only on high. It's usually located under the dash, relatively easy to access and replace.
* Blower Motor: If the resistor is okay, the blower motor itself could be failing. This requires removing it from under the dash and testing it.
* Blend Door Actuator: This is the most common cause of inconsistent heat. It's a motor that controls the blend door that mixes hot and cold air. These can fail, stick, or become noisy. Accessing and replacing it requires partial dash disassembly, and it can be challenging depending on your experience level. Sometimes, lubricating it can solve the problem temporarily.
* Vacuum Leaks: Check all vacuum lines related to the HVAC system. Leaks will affect the operation of the blend doors and other air control mechanisms.
* Air Distribution Flaps: These can become stuck or broken. This usually requires more in-depth disassembly.
3. Repair/Replacement:
* Many parts are available at auto parts stores. Be sure to specify your 2002 Chevy Blazer's engine size (e.g., 4.3L V6) when ordering parts.
* Repair manuals (Haynes, Chilton, or online resources) are invaluable for detailed instructions, diagrams, and torque specifications. These are crucial, especially for more involved repairs like replacing the heater core or blend door actuator.
* Consider taking your Blazer to a qualified mechanic if you're not comfortable with automotive repairs, especially those involving dash disassembly. The cost of professional repair might be less than the cost of damaging something while attempting the repair yourself.
Important Note: Before disassembling anything, disconnect the negative battery terminal to prevent electrical shorts.
This is a general guide; the specific repair will depend on the exact nature of the problem. Accurate diagnosis is the most important first step. Remember to consult a repair manual for detailed procedures and safety precautions.
