Heater Fan Failure
 

I hope this is not too mundane an issue for this forum. The heater fan has stopped working on my 2004 Honda Civic with 267K miles. I have checked (and swapped) the fuse without effect. Since the car is in generally good condition and runs very well I'd like to resolve this problem but I'm a bit concerned about the expense. I am not particularly mechanical so I'm looking for any guidance.

what year and model is that car? do any fan setting work? youre gonna wanna check the switch, wiring, relays, fan resistor, motor.

Locate the fan switch. Should be on the Tstat housing that is on the motor side of the lower hose. Unclip the fan switch and stick a paperclip in it to connect the two wires together. Turn the key to (ON), no need to start the car though. If the fan comes on at that point, the fan switch is dead.

If not, you can try the relays by swapping them around (located in the fuse box of the engine bay I believe), otherwise, the fan motor is dead, or there is a wiring problem.

It is a 2004 Civic LX ... thought I posted that originally. CV, I'll go looking when I have the car again (the bride commutes in it) but may have to come back for more specific locational directions. :-)

No problem. IIRC, there should only be one plug on that housing, along with a ground wire bolted to the housing, too.

Just checking in to say that I haven't had access to the car when I've had time to look at it. For a woman who hates fresh air to blow in the windows (and loves her air conditioner) my wife seems intent on keeping me from the heater fan! I guess I should be thankful ... I love the wind to howl through as I drive. :-)

Wait. What do the windows have anything to do with the heater fan?

I am starting to think you are not talking about the cooling system of the vehicle anymore. Are you talking about the blower for the climate control in the car, or the fan in the engine bay that prevents the car from overheating in traffic?

One of those are essential to the car (radiator fan), another can be ignored if you want (blower motor).

Um, I'm talking about the fan for the climate control, "Heater Fan", not the radiator fan. I guess I should have taken the automotive class in high school, sigh.

Well, my apologies for the misunderstanding. Completely ignore everything I have said before.

With something like this, you are probably going to have to get under the dash and test the wires to see if there is a wiring problem, or if the motor in the blower assembly is dead. Shouldn't be too hard to replace the blower if you need to. I did it for my brother's 98 Civic in about 45 minutes taking my time. I am not good with actual electrical problems, so my bad if my help seems vague.

Usually the problem there is the power transistor. Find the motor under the right end of the dash (no need to take anything apart), it has a 2 wire plug on it. Turn key on and set switch on high. With plug still plugged in, measure the voltage from each wire to ground.

Zero on both: check fuse and relay under the hood.
12 on one, close to zero on the other: motor is bad.
12 on both: Most likely the power transistor. Could also be the control panel, but that is rare.

Before replacing power transistor, remove the motor / fan assembly and check for mouse nest in the ductwork.