1. Simple Checks (Before diving into complex repairs):
* Is the engine warm enough? The heater only works when the engine coolant is hot enough. Let the engine run for a good 10-15 minutes before assessing the heater.
* Are the heater controls set correctly? Make sure the fan speed is on, the temperature is turned up to hot, and the heater controls are directed towards the cabin (not defrost or floor only).
* Is there sufficient coolant in the system? Low coolant means the system can't effectively transfer heat. Check the coolant level in the radiator's overflow tank. Caution: The engine and coolant will be hot; allow them to cool before checking.
* Are the heater hoses hot? Feel the two hoses leading to the heater core (usually located behind the dash). If both are cold, there's a problem with coolant flow. If one is hot and one is cold, there's likely a blockage or problem within the heater core itself.
* Are the fan motor blades obstructed? If you can access the blower motor (usually located under the dash), ensure the fan blades aren't blocked by debris.
* Are the fuses and relays intact? Check the fuse box for blown fuses related to the heater fan or blower motor. Your owner's manual will show you which fuses are responsible. Relays are also electrical components that can fail; your owner's manual will be needed to properly identify and check those.
2. More Involved Issues:
* Heater Core Problems: The heater core is a small radiator that sits inside the cabin. It can become clogged with debris, rust, or develop leaks. A leak will result in coolant leaking inside the cabin. Replacing a heater core is a relatively involved job requiring dashboard disassembly.
* Blend Door Actuator: This motor controls the flow of air between the heater core and outside air. A faulty blend door actuator can prevent hot air from reaching the vents.
* Water Pump: A malfunctioning water pump doesn't circulate coolant properly. This will lead to insufficient heat throughout the entire cooling system.
* Thermostat: A stuck closed thermostat will prevent coolant from circulating until it reaches a very high temperature. This means the heater won't work until the engine is severely overheating (which should be avoided at all costs).
* Wiring and Electrical Issues: Problems with the wiring harness leading to the heater blower motor, heater control switch or other components can interrupt the flow of electricity.
Troubleshooting Steps:
1. Start with the simple checks listed above. This will save you time and effort.
2. If the simple checks don't solve the problem, move on to checking the coolant hoses for hot/cold and proceed with further diagnostics.
3. Consider a repair manual specific to your 1992 Chevy G20. These manuals provide detailed diagrams and instructions.
4. Consult a qualified mechanic if you're not comfortable performing repairs yourself. Diagnosing heating system issues can be challenging, and improper repairs can lead to further complications.
Remember safety first! Always work on a cool engine and use appropriate safety precautions when working on your vehicle's cooling system.
