Why is this happening?

[00QX4garn]

2000 QX4, I can't seem to turn off AC fan.

https://youtu.be/EBJ9C71gwJo

[Towncivilian]

Welcome to NICO.

Please try performing self-diagnosis described on page HA-37 of the factory service manual.

[00QX4garn]

Self diagnosis didn't tell me anything. So, this never happened to anyone else? Could this be a bad blower motor resistor?

[Towncivilian]

This thread is the only one that relates to your issue, but unfortunately everybody in the thread misdiagnosed the problem as the blower motor resistor, when the auto climate control system uses a fan control amplifier (see its location here). This is a more expensive, but still failure-prone part. I believe you should try replacing this part first. You can give Rob a call at 1-866-742-0297, he should be able to provide you with the best price for an OEM part. Have your VIN ready.

You may wish to change the cabin air filters while you're replacing the fan control amplifier if they haven't been changed within the past two years. No need to get OEM filters here, aftermarket ones from your local auto parts stores are cheaper and will work just as well.

[00QX4garn]

Got new blower amplifier, removed glove-box, replaced it. no change. what else could it be?

[Towncivilian]

I would think auto HVAC control unit next. I don't think there's a way to narrow it down at this stage, unfortunately. Trying to find a used unit at a junkyard is your best bet.