Do all heated seats have relays?

[Colesy]

I've been looking at the heated seat loom from the S4 I used to have and the wiring seems to be missing any where for relays.

The loom I have has two green plugs that plugged into the seats. Two brown plugs that plug into the switches. And 3 wires that come off this loom - Earth, live and ignition (I assume). There are absolutely no wires that have been cut off this and it doesn't seem to match any of the looms discussed on here before such as in this thread:

http://www.s2forum.com/forum/showthread.php?t=15583&highlight=heated+seats+loom

Picture:


Any help much appreciated.

[Error404]

I think the later looms use different switches with relays built into them

[djh]

as error said

[mcandmar]

Yup later cars had the relay inside the switch, the switch itself is almost twice as long.

[Colesy]

Cheers guys, looks like that's what I've got.

Does anyone know how to test the switches? I don't have the heater inserts for the seats and while the switches light up they don't send power to the seats. I am guessing that there is some sort of temperature sensor signal required to go to the switches before they will send power to the heaters?

[UrS4boy]

C4 Heated Seat Harness diagram

I think you have your answer (which is good) because the info that I have, the diagram below, doesn't show any provision for connection into any relays:

[UrS4boy]

Cheers guys, looks like that's what I've got. Does anyone know how to test the switches? I don't have the heater inserts for the seats and while the switches light up they don't send power to the seats. I am guessing that there is some sort of temperature sensor signal required to go to the switches before they will send power to the heaters?

The front seats have some kind of temperature sensor to prevent over heating. The rear seat heaters have a microswitch that requires some weight, e.g. a person, to be in the seat before the power flows to the heater elements.

[Colesy]

Cheers for the diagrams, there's not a wiring diagram for the heater loom plug is there?

[UrS4boy]

Cheers for the diagrams, there's not a wiring diagram for the heater loom plug is there?

Sure. Pages 12/48 and 14/48 of this 97 A6 wiring diagram:

http://12v.org/urs/1997_Audi_A6_Syst...g_Diagrams.pdf

If that doesn't work, you could try looking through this:

http://www.ziomal.itl.pl/motoryzacja/download/audi/Audi_A6_96_schematy.pdf

[Colesy]

Legend, your first link pg14 has the exact diagrams of the loom I have. Any idea how the temperature sensor might work? Would it be safe to link the two sensor wires to simulate the sensor working properly?

[UrS4boy]

Legend, your first link pg14 has the exact diagrams of the loom I have. Any idea how the temperature sensor might work? Would it be safe to link the two sensor wires to simulate the sensor working properly?

Sorry. I don't know how it works. All I can tell you is that when you dial the heater reostat control to 5 (out of 6) it gets hotter before it shuts off (temporarily) than if you set it to 3 (out of 6). On that basis, I imagine it is measuring a resistance relative to the resistance in the reostat setting. I don't think you can simulate it. However, if you are trying to test the loom and the heater element, that temp sensor should be closed when there is no power to it. From what I see, it looks like the temp sensor disconnects the power via the solid state controller/relay when the set "temp" resistance) is met by opening up that leg of the circuit, i.e. Pin 3 to Pin 6 ground. When things cool down, the temp sensor closes again and the heating cycle is repeated.

Note that the heater element supply circuit is on one fuse (30A, the red/white stripe wires) whereas the control circuit (Black/blue stripe wires) is on two (?) 15A fuses (in series (huh??)). Note also that the heater elements are in series, i.e. if a wire in the seat bottom element breaks, there is no power the the seat backrest element either. Bugga.

[newsh]

I think 15a on the "central electric panel" is a busbar, not a fuse.

If the seat and back heaters were in parallel you would need a switch and thermostat for each. Otherwise if the seat element went o/c the back would get very hot.