2007 Freightliner century ac blower motor will not shut off

If the blower motor will not shut off when you turn the switch to the off position then the blower is still receiving power, obviously. Now, where is that power coming from?

I suspect that the blower motor resistor is shorted and applying power to the blower and keeping it on.

Disconnect the electrical connector to the blower motor resistor and see if the blower shuts off. If it does shut off then the resistor has shorted and is the culprit. If it does not shut the blower off then the blower is still receiving power from somewhere.

I would start by unplugging the blower motor resistor and posting your diagnostic findings here when you're done.

 

Note: Under normal operation the blower motor will still operate on high only when the resistor is bad or unplugged. Resistor operates the lower settings only. For what it’s worth, no fan on all settings usually means the fan is bad. Often operation is intermittent. Just had that happen on a Volvo. On the other hand, if fan only works on high, usually means a bad resistor. I already mentioned that. The question is why both are affected? Might be hard to find the problem. Maybe ignition related. Just guessing. Hopefully someone else has had or seen the same issue. The plugs for the switches are known for getting hot and melting. Usually only the bunk switch. Be a good place to start. Might have to just put a toggle switch inline on the hot wire to each switch. Rare chance both plugs are melted. They get hotter as the fan gets older and spins slower, often melting before the fan finally quits.

 

I'd think if the resistor was shorted. He wouldn't have variable fan speed.

 

Iirc, the body module controls the fan, that can be defective. There should also be a relay for the fan somewhere among the hundreds (*sarcasm) relays, read the owners manual to find which one.