Blower fan connection has low voltage

[Mbn42]

The blower fan was not working. Fuse ok, so pulled out the fan to replace. I tested fan by connecting to 12 volts from battery, it was ok. This is where  I got out my multimeter. I have low voltage at the main wires for the blower fan. I have full voltage at the fuse, and confirmed I had the correct fuse (removing fuse makes voltage go to zero). I can’t see any wire damage, wiggling wires has no effect on voltage. So, is there some resettable fuse or other device between the fuse box and the blower motor that could be faulty?

[Mbn42]

Attached some pics of diagnostics, correct voltage at fuse, low voltage at connection 

[Breezy_Pete]

Yes, there's a resistance to control the speed of operation. Might be a conventional wirewound resistor with multiple tappings for different speeds, or a transistorised version, depending on A/C controller type. 

[Mbn42]

The resistor unit is in the pic below, bolted to the fan unit. The  brown and red/white wires in the plug (other pic) should have 12 volts all the time I think (but don’t) and the climate control buttons in the cab, when adjusted, send a different voltage signal to the resistor unit. I have verified that the voltage for one of the thin wires in the plug changes as climate control buttons are adjusted. 
I also think that if the resistor unit fails, the fan should work if put on full speed? Which it doesn’t.

that leaves me thinking there is a problem between the fuse box and the plug connection. 
 

I’ve gone one step back in the loom to check the last section of wiring is ok, seems fine.

[gasgaraget]

Have you checked with a different ground when measuring at the connector. So you know if it is the feed or return path you are loosing voltage? Could it be a bad ground through another circuit? (Return path)

[Mbn42]

Good suggestion. It is definitely the positive wire (red/white). I have a feeling if I ran a new positive line with a fuse to the connector and cut it in, it would be easier than taking off all the dash to try snd find the problem. Unless there is a known problem or component that I should be looking for?

I should note that the lower voltage I see at the red/white wire is constantly bouncing around by 0.2 volts or more. Not sure what it means.

[Mbn42]

If there was a wire chaffed like shown in this other post, could that be a potential cause consistent with low and variable voltage?

 

[Mbn42]

Are there any relays or other devices between the fuse box and the blower fan that people are aware of? I haven't found a free wiring diagram for the Skoda Superb II, and if I did, I might struggle to work out what it means!

[Breezy_Pete]

What year is the car please?

[Mbn42]

2014

Full details:

Year: 2014
Make: SKODA
Model: SUPERB
Colour: BLACK
Submodel: 125KW4X4ELEGANCEW 2.
Body Style: Station Wagon
VIN: TMBMF93T1E9011439
Engine No: CFG385324
CC rating: 1,968cc (2.0l)
Fuel Type: Diesel
Drive: 4WD

[Breezy_Pete]

OK, ta.

 

According to circuit info, fuse 22 (40 Amp rated) is permanently/directly powered from battery positive, and there is no other device between the fuse output wire (black/red 4mm²) and the 6-way beige connector you have in the last photo, except a 10-way intermediate connector where that black/red from the fuse changes to the red/white that goes into the beige connector. 

 

Location of this intermediate connector described as 'behind dash panel', rather unhelpfully. Finding this connector and checking for corrosion of contacts may be what you need to do.

[Mbn42]

Thanks very much! That is very helpful. In the last picture I posted, you can see the 10 way connector where the wire colours change in the top right corner. I pulled that apart, no corrosion, same problem with the lower voltage.

My job for the weekend will be to run a new wire with a fuse to the fan and see if that resolves the problem. Any suggestions on where I should tap the positive from?

[Kevgem]

did you get to the bottom of the problem you where having with your blower motor? i am getting the same problem

cheers kev

[Mbn42]

I ran a new wire from the fuse box to the fan. It should be of an appropriate gauge (25amp), and obviously ensure fuse is still in the circuit. Working fine new.

[Kevgem]

cheers buddy!