* Blend Door Actuator: This is a common culprit. The blend door actuator is a small motor that controls the mix of hot and cold air going into the cabin. If it's faulty, it might be stuck in the "cold" position, even if the coolant is hot. You'll need to check this, potentially replacing it. It's usually located under the dashboard, often requiring partial disassembly to access.
* Heater Core: The heater core is a small radiator located inside the car that warms the air. It could be clogged, leaking (which would leave a sweet smell in the car), or even completely failing. A leak would be evident by wet carpet on the passenger side floor.
* Heater Core Hoses: Inspect the hoses going to and from the heater core. Make sure they are connected properly and not collapsed or kinked. Ensure there's good flow. If you can feel heat in the hose *going* into the heater core but not coming out, the heater core is suspect.
* Vacuum Lines: The system may use vacuum lines to control the blend door. Inspect these lines for leaks, cracks, or disconnections. A vacuum leak could prevent the blend door from moving correctly.
* Temperature Control Cables (If Applicable): Some older vehicles use cables instead of electric actuators. Check for broken, frayed, or disconnected cables.
* Coolant Level (Again): Even though you replaced the water pump and thermostat, double-check the coolant level in the radiator and overflow tank. A low level can still hinder heating performance. Also, ensure there are no leaks in the system. A pressure test might be necessary to rule out a slow leak.
* Wiring/Fuses: Check the fuses and wiring related to the heater system. A blown fuse or a short in the wiring can disable the heater.
Troubleshooting Steps:
1. Feel the hoses: Feel the hoses going to and from the heater core. If one is hot and the other is cold, the heater core might be the issue. If both are cold, the problem is likely before the heater core (e.g., a clogged system or a faulty thermostat (double-check your thermostat installation!)).
2. Listen carefully: With the heat on, listen near the heater core area. You might hear a whirring sound from a working blend door actuator. If you hear nothing, that's a prime suspect.
3. Check the coolant temperature: Ensure the engine is getting up to operating temperature. A malfunctioning gauge is possible, so feel a hose near the engine to verify heat.
Important Note: Working on the heating system often involves accessing parts under the dashboard. This can be complex and requires patience and some mechanical aptitude. If you're uncomfortable disassembling parts of your car's interior, consider taking it to a qualified mechanic. Ignoring a heater core leak can lead to significant damage to your car's interior.
