A/C blower motor stays on, even when car is off

Check the 12v battery

 

Well, that's sort of entertaining.

At first I would have bet that the power supply to the blower was switched with the ignition and so that Couldn't Happen.

But according to the diagram, the power coming in on the black wire (position 3) comes from a fuse that has power always.



The blue wire, position 2, carries a variable pulse train that is sent by the A/C amplifier, telling the blower how fast to spin.

When the car is off, presumably the A/C amplifier doesn't send pulses.

I'd assume it's most likely that the control circuitry inside the blower motor has failed, and now it just continues to run even when the A/C amplifier isn't sending it control pulses.

On the other hand, it might be fun to scope that blue wire with the car off; perhaps it could also be that the A/C amplifier is misbehaving, and sending control pulses when it shouldn't be.

Edit: nuts, I was hoping to get an answer on the board before somebody jumped in with checking the 12 volt battery.

Then again, you probably do want to check the battery anyway, if it's been running this blower overnight.

 

In your first post, you mentioned a blower motor resistor, but no Prius ever had one of those. In the first couple of generations, there was a separate module (active electronics, not a resistor) that would take the desired-speed signal from the A/C amplifier and convert it to driving voltage for the blower.

As you can see in the Gen 3 diagram, that is just built into the blower motor now. It has a connection to battery (always on), and to ground, and to the blue SI signal from the A/C amplifier, telling it how fast to spin.

So there's a couple possibilities here. One, the A/C amplifier is ok, it is not sending pulses when the car is off, but the blower motor electronics have a problem and now run at some nonzero speed even when not receiving pulses.

Two, the blower motor might be ok, but the A/C amplifier for some reason is sending pulses even when the car is off.

You should of course make sure the battery voltage is reasonable before trying to distinguish possibility one from possibility two.

Simply scoping that blue wire when the car is off but the blower is running should give all the information needed to pick one of the two.

 

I would check the battery anyway cause everything is made cheap nowadays

 

Pretty much anything that would show you there are or aren't pulses happening on that wire I think would do the trick. This is not going to be the kind of diagnosis that hinges on nuances of the wave shape.

 

The Prius has the option of running the A/C while the car is off.

 

When you activate the remote A/C feature, the car actually turns on (that's why there are warnings in the owners' manual that the wipers, headlights, etc. might come on too); it has to, because the A/C compressor itself is powered by high voltage from the traction battery, which is isolated when the car is off. Really none of that is what @BigFatGuy described in the original post.

BFG, where did you get the blower motor you put in back in summer 2020?

 

Doesn't sound to me like a ringing endorsement of Rock Auto for blower motors.