seat overheated

[ruud1968]

I recently experienced a serious problem with the (heated) driver seat on my 2004 Transit minibus 100t300. It can get really warm when the heater is on, and I mean it will burn you. I have several burn marks now on my leg, before I noticed the seat was smoking hot.

This is not funny, has this problem been reported before (could not find it)? What is causing this? I accidentally had selected to turn on the heater 1 week before, but at low temperatures it would not work, I think. 1 day the weather was less cold and it worked. The seat is also burned now with a hole in it.

I am not turning this on again....

thx, ruud

[ake]

The timer or thermostat is faulty and not cutting off

[Timbo]

I don't think there is a thermostat as such on the heated seats (none shown on TIS wiring diagrams). I believe the heater wires are supposed to be self regulating. When the enement gets hot then its resistance increases.
Does the squab over heat and the back remain cold ?
The two sections are wired in series i.e. power goes through one then the other.
Check the wires that go between seat squab and back as if they are shorted together the squab will get too much voltage and probably overheat.
Could also be damaged wires or elements shorting to the seat frame.

Hope your b*m recovers.

[Nadjenka]

Timbo, I wouldn't know much about what kind of wire is fitted in Transits, BUT:

Self regulating cable does not overheat under any circumstances. Self regulating cable basically runs + and - wire encased in paste that melts as the temperature increases. Once melted heating stops, until the paste goes hard again. If self regulating cable gets shortened, it will not work anymore. Also self regulating cable looses it's power over the time, gives out less heat over the years.

By the sound of it, I would think it is standard 12v heating cable fitted via regulator and relay - which apparently doesn't work. This kind of cable will keep getting hotter and hotter until it eventually burns itself thru. This happens when there is some insulation layer blocking the heat (in this case OPs bum ). However - it's weird that the cable would not shorten out before it burns thru the seat Once the cable reaches around 50 degrees it should melt the insulator layer and shorten/cut out. There will not be thermostat controll for it.

This answer probably doesn't resolve anything, but I would be looking at the heat regulator switch and relay as it seems to be not working. OR - stop eating spicy food

[Nadjenka]

Thinking about it a bit more - Timbo, isn't there thermostat at the end of the cable (if you are looking at Tis)? Some people would call it self regulating cable too - it's standard heating cable with thermostat control at the end of it (so it might not be displayed as part of the wiring - it's part of the cable). I wouldn't expect it to be fitted in a heated seat though... The thermostat at the end of the cable is normally factory pre-set to certain maximum temperature. If this would be installed in a seat and the end of the heating element slipps out (hanging down under the seat or something) the thermostat at the end would not be able to read correct temperature of the seat. That would cause the cable to overheat, but tbh I really would not expect this type to be fitted in heated seats... Haven't even seen 12v version of this one yet

[Timbo]

Looking further on TIS at the Mk 5 heated seats diagram there could be seperate thermostats in each section (mk 6 only shows heater elements), so either squab or back reaching temp first will shut both off.
I still go for a short to seat frame or shorted wires on back section. I like your idea of the stat falling out of seat but the one in the backrest should still cut the power to both sections.

[Nadjenka]

Not necessarily If there are two cables connected in a paralel, then I'd think they have each it's own stat. This is what the thermostat control looks like on 240v cable version. It's all in one piece.

[Timbo]

Sorry to disagree (please don't hit me next time we meet) but each seat has its squab and backrest wired in series so either thermostat getting to temperature will switch off both sections, unless there is a fault - stuck thermostat or shorted wire.

Power goes from switch to the squab heater then to backrest heater and then to earth (chassis).

[Nadjenka]

Don't be sorry, I don't know what is fitted, and I would like to know. I am gratefull for the info you are posting Timbo I misunderstood the first post of yours

The two sections are wired in series i.e. power goes through one then the other.

I understood that it would be TWO circuits connected in paralel to the relay that sends power separately to the seat and backrest, rather than one circuit. My bad

Power goes from switch to the squab heater then to backrest heater and then to earth (chassis).

Could you scan the diagram for this please? Shouldn't the power go back to the swith

[Timbo]

I would post a diagram if I had the slightest idea how to do it, I can't even manage to get smileys on my posts..................

[Nadjenka]

No worries, I'll send you pm with my e mail, can you send it there? I'll post it up then.

Still - I have never seen heated transit seats nor the diagrams for them, only looking at car seat diagrams online and it would seem to be that all factory fitted heated seats are wired to the thermostat (coupler) fitted in the seat before the wire returns to the earth What protection would there be if it's wired directly to the earth? If only one coupler is fitted in the Transit seat, then if it fails - the overheating can occur. But how would bad earth affect that? Wouldn't that just short it out altogether?

[Timbo]

Apologies to Ruud1968 for highjacking your post but we are trying to find the reason for your overheated posterior......

[Nadjenka]

Thanks Timbo Here is your diagram:



It makes sence... Now we need the answer to if the back was heating up or not at the same time as the seat was

[ruud1968]

Apologies to Ruud1968 for highjacking your post but we are trying to find the reason for your overheated posterior......

no problem, interesting reading material. i'll take a look this weekend, maybe take a picture of the chair and the wiring. won't try to fix it

[ruud1968]

It makes sence... Now we need the answer to if the back was heating up or not at the same time as the seat was

seemed a local problem. it was not the back, only the cushion on the side of the seat close to the door. burned a hole and smoke escaped from a small 'pipe'. too bad I was sitting on it.

thx, ruud