* Blend Door Actuator: This small motor controls the direction of air – whether it comes from the heater core (hot) or the AC evaporator (cold). A faulty blend door actuator can prevent hot air from entering the cabin even if the heater core is working. This is a common culprit.
* Heater Core: The heater core is a small radiator that warms the air. It could be clogged, leaking (resulting in a sweet smell in the cabin), or simply not getting enough coolant flow even if the hoses are warm. A restriction somewhere in the heater core circuit is possible.
* Water Pump (less likely): While you say the hoses are flowing, a weak water pump might not be circulating coolant efficiently enough to adequately heat the heater core. Check if the upper radiator hose is significantly hotter than the lower one. A weak pump would show a larger temperature difference.
* Coolant Level: While you've addressed the thermostat, ensure the coolant level is correct. Low coolant will prevent efficient heating.
* Wiring/Fuses: Check the fuses and wiring related to the heater system. A blown fuse or faulty wiring can interrupt power to the heater blower motor or the blend door actuator.
* Heater Blower Motor: While unlikely given you have AC, a faulty blower motor resistor or the blower motor itself could prevent air from blowing, regardless of its temperature.
Troubleshooting Steps:
1. Check the blend door actuator: This is usually accessed under the dashboard. You might hear a clicking sound when you switch from AC to heat, indicating the actuator is trying to work but failing. Replacing this is often a relatively straightforward repair.
2. Check coolant level and hoses: Ensure the coolant level is correct and the hoses leading to and from the heater core are warm (not just lukewarm). If one hose is significantly cooler than the other, there's a restriction somewhere in the system.
3. Check the heater core for leaks: Look carefully under the dashboard and carpets for evidence of coolant leaks. A sweet smell is a telltale sign.
4. Check fuses and wiring: Consult your owner's manual to locate the fuses and wiring diagrams related to the heater system.
5. Listen to the blower motor: Does it sound normal? If it sounds weak or makes strange noises, it might be failing.
If you're not comfortable working on your vehicle's HVAC system yourself, take it to a qualified mechanic. Diagnosing heating problems can be tricky, and a professional will have the tools and expertise to pinpoint the issue efficiently.
