2004 Accord No Heat

Question

My son has a 2004 Honda Accord EX 2.4L.  The interior heat stopped working and he can't defrost his windows in the morning.

Here are the things I've done to fix the problem:

Replaced the thermostat
Replaced the water pump
Replaced the radiator (it was old and in bad condition)
Back flushed the heater core -- it flushed out with no issues
Back flushed the entire cooling system -- no apparent issues

Having done all of this, there is still no heat coming from the interior vents in his car.  After running the car hard for a while, the top radiator hose gets hot, but the bottom does not.  This makes me think the thermostat is not working, but I tested it in boiling water and it does open.

Any help would be appreciated.

DavidSupportsMonica · Answer

Within the heater assembly is a small door that routes incoming air either directly into the car's interior, or through the heater core to be heated before entering the car's interior, or something in between to allow airflow through both paths. It's usually called the "blend" door, and it's likely stuck in the "no heat" position.

I'm not familiar with the '04 Accord EX, and don't know how the blend door is controlled. There may be a rotary knob on the dashboard which connects to the door via mechanical linkage or a bowden cable. A more complicated variant uses a vacuum-operated actuator at the blend door to move the door; the driver uses pushbuttons or a rotary control on the dash to choose where vaccum is routed, and thereby open or close the door and change the air path. Another possibility: the car's heating system may automatically regulate the air blend by sensing the car’s interior temperature, and adjusting the blend door position using an electric actuator at the door.

You'll need to locate the blend door, confirm that it’s not moving, and troubleshoot the cause.

2004 Accord No Heat

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