How to bench test R blower?

Hi everyone!
R blower stopped working. B4 fuse is good in the R fuse panel, relays click. No visible sign of cracked solder joints or burned wires. According to the wiring diagram, it gets power through the brown plug. When I apply 12V, nothing happens. Is this how to test the blower or it needs the white plug to be connected to work?
Thanks for any help in advance.
P.s.: I did the test when the wires were connected to the blower motor.

You should be able to power the motor directly to make sure that is working, after that its possibly the Darlington (?) (it’s been a long time since I was in one of those)

Hi Robin!
I forgot to mention I tested the motor directly and it runs. I haven’t replaced the Darlington transistors in the blowers yet. Is there a direct replacement or what would be the correct one?

HI Joseph, as I said it’s been a long time since I was there, I am sure if you use the search function there will be all the information needed to refurb the resistors.
Here’s just one;

Thanks Robin, I’ll search the archives.

The list of parts I used (almost 8 years ago) are in the eBook on the old site – here’s a link to it Joe - almost all electronic stores will have the parts - Mouser is who I used IIRC

Thanks for the link Larry. I was wrong before. After a closer inspection, I noticed a cracked solder joint at the leg of the Darlington transistor. I’ve reflown both of them. I’m gonna plug in the blower in my car and see if it runs.

Not sure Joe but I think it should still run on high even if the big transistor is Kaput?

I don’t know that either Larry. I’ll report back after testing it in my car fully plugged in.

Well, I reconnected the blower and still nothing at any speed. Gotta look deeper into the diodes and transistors.

What about those 2 blue relays in there Joe? Did you have a go at them?

When I did my blowers, those relays were VERY pricey so I think I used a regular el-cheapo one and soldered a diode on the outside to make it like one of the originals.

I just tested the relays and they click.

I ordered a 2n6284 transistor from ebay for $8.95. Will report back after replacing it.

I rebuilt two of my blowers that had failed and both times it was the large Darlington transistor that was at fault. Actually I purchased all the electronics (i believe there are 4 with the diodes) and being lazy only replaced theDarlington both times. That was years ago and no problems since.

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Thanks Grooveman. At this point I can only hope it’s the Darlington transistor. I know hope is not a strategy but I can’t do anything right now just wait until I get it and see what happens after replacing it.

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I installed the new transistor.

The innards of the old one made by ST Microelectronics:

The brown plug in the picture has positive and ground whenever the key is turned on. If the blower runs without the white plug connected, it probably has a shorted out transistor. It should not run until the controls tell it to and these go through the white plug. The relay overrides the transistor and puts full power to the motor. It can run at full speed without the relay. Both blowers should work in unison. If one works and the other does not, after verifying that it has power, it is probably the blower circuit vs a problem in the car.

Thanks Dick. I thought the white plug needs to be plugged in to make the blower to work. I’m gonna put the blower back together, install it and report back.

Any update on the situation there, Joe?

Larry, I replaced the Darlington transistor but having a trouble make the flap door to work. That plastic gear broke so the door won’t stay in place. Trying to attach a pivot arm to the flap door but it won’t just stay on. I tried JB Weld and soldering but looks like it has to be welded on.