Some may be aware that early this year I decided to have a look at the function of the heated seats, as many including myself were very unhappy at their performance. I discovered a few things about their operation and that of the switch that others may also find useful.
I have to add that I had lots of information from others to help, and I thank Frenchmike, Trebor, Stocktake and others for their help and input.
I will give some facts about the standard operation and why the performance is inadequate.
Firstly the switch,
I spent much time testing and retesting the switch as well as taking the thing apart to try to work it out.
The switch appears to be quite a reliable electronic device using various IC's but it definately has an electronic timer in it of about 15 mins or so. But once the timer mechanism has switched the seat off, it will immediately switch the seat heater back on if it is repressed.
Secondly,
the heated elements have two thermostats in them. One in each element. These thermostats are rated at 40c, but mine and others that have also tested them, they cut out at much less (around 32-34c).
Once the temperature has been reached at either part of the seat, one thermostat will cut out and will not reset itself until the seat temperature gets below about 15c. This means in practicable terms that all the time your bottom is on the seat it will not reset. So once 32c or so is reached, the seat will remain at approx 25c or whatever temperature your bottom is.
Thirdly,
The leather on my seat is thick and it takes about 5 mins for any heat to transfer through the leather to where I can feel it.
So, in finding a way of improving the seat, I had to discount anything with the switch, as this is not the real problem. Sure, it might be possible to change one of the microresistors that would extend the timer but the switch is tiny and I do not have the electronic knowledge to do it.
Even if this were done it would not stop the thermostats in the elements tripping.
So, I started looking around for bi-metalic thermostats that might replace the originals in the element pads.
After trying a few, I have now had some positive results from some that I got from Hong Kong.
They are 45c(normally closed) thermostats that reset themselves at about 29-30c.
The advantage of these thermostats is that the resetting temperature does not require your bottom to leave the seat, and will happily cycle from 30c to 45c permenantly, providing the heated switch is turned back on every 15 mins or so. And you have to remember that 30c is close to the hottest of the current thermostats.
So luckily changing the thermostats does not require you to strip the seat cover and can be done relatively easily with either soldered or crimped connectors.
The back board does need to be removed, and this is the trickiest part.
I would say each seat takes around 30-45 mins and at the end you would feel a definate improvement.
How to change the thermostats:
So to start with, the backboards need to be removed.
Here is a how to by Devilish which I followed
http://www.the75andztclub.co.uk/foru...ad.php?t=60562
Although I did unclip the 4 side clips first and then the bottom ones, as I found it easier to be able to see what I was doing with the bottom clips with the sides free.
Next step is to unclip the leather from behind the backboard. These are just 3 moulded plastic clips that easily unclip from the metalwork. Once this has been done the clips and the leather just feed between the base and back. Then a little bit of rolling up of the leather on the bolsters will reveal the thermostat. It is under a bit of fabric which needs to be gently prized up. The stat is glued to the element pad and can be prized off very gently or heated up to melt the glue. The old stat needs to be unsoldered and the new one resoldered. I will add at this stage that it would be possible to just solder the wires together and rely on the base stat, but I feel the extra security of 2 stats is worth it as the cost of the stats is so small.
The other point is that I think is worth mentioning is that I feel the metal part of the stat should touch the element and not the foam, and not as I had it in my picture. I think this makes it cut out slightly earlier, and we have to remember that the elements will be getting much hotter than before and for longer than before.
Next the base stat, which is very easy to get to. If you follow the leather behind the seat you will see three black plastic mouldings attached to the leather. Again these just pull off the metalwork and they and the leather once again feeds up between the seat base and back. This will reveal the base stat, which just needs to replace the existing one.
Again my recommendation is to have the metal of the stat touching the element and not the foam.
I will add when feeding the leather through between base and back, using the reclining mechanism to a differing position may help.
Also when accessing the stats, the seat position may need to be moved to help access.
If you wish to test the temperature as a safety check, then on completion a thermometer could be placed between your bottom and the seat and read as the temperature rises and falls. It takes about 10 mins for mine to cut out and maybe another 10 mins for it to automatically start heating again. But your seat should not drop below about 29c.
I will add that I have tested my elements to 50c with other stats and they have not failed for me.
But my advice is to check that the temperature does not get this high and cuts out somewhere between 40c and 48c.
Obviously this modification does carry a risk of damage or failure, and I will not be held responsible for this. I am just describing what I have done to my car and why.
Hope this is of some help, as I say about 45 mins work for each seat and then considerably hotter seats. Sit back and enjoy.
Matt
Photos of:
Back of seat without backboard showing leather to be fed up between back and base.
Old thermostat.
New thermostat soldered on (but stat needs to be upside down and not as in photo).
