Extend Heated Seat High Time - PeachParts Mercedes-Benz Forum

Rick76 · #1 03-04-2009, 08:09 PM

I always found that the time that the heated seats stayed on high was too short. By changing the value of two resistors the time can be increased from 4 minutes to 11 which I find perfect.
Look for two 84500 ohm resistors (gray,yellow,green,red,brown). By changing these to 200K ohm, the time increases to 11 minutes.
These details apply only to the 126 820 18 26 heated seat control module (used in 124, 126 and others) but other modules can probably be modified as well.
Next step is to add a thermistor so the time varies with vehicle temperature (maybe next winter).

pawoSD · #2 03-04-2009, 08:55 PM

Cold seats are what separate the boys from the MEN.

babymog · #3 03-05-2009, 11:43 AM

Thanks for the info, I might try this modification.

Honestly I don't know why it times out at all, I'd rather it stays on (and the rear defrost) until I turn it off like my Audi seats/window. Turn that sucker to six and it's really nice (109F IIRC on 6).

Just one of the little inconveniences.

pawoSD · #4 03-05-2009, 01:14 PM

Quote:

Originally Posted by babymog

Honestly I don't know why it times out at all, I'd rather it stays on

Maybe the engineers were worried about people's rears getting a little overdone!

Ferdman · #5 03-05-2009, 02:49 PM

Rick, instead of modifying the circuit it's a lot easier to press the seat heater button again so it's on high. My wife typically does that a few times so her butt is toasty.

pmckechnie · #6 03-05-2009, 04:19 PM

Rick
Thanks very very much. I really think this is a great idea and I will be making this modification. It seems others don't appreciate good tips like this. I DO.

Paul

Rick76 · #7 03-05-2009, 04:48 PM

Quote:

Originally Posted by Ferdman

Rick, instead of modifying the circuit it's a lot easier to press the seat heater button again so it's on high. My wife typically does that a few times so her butt is toasty.

I've been pressing the button twice for 11 years. No more!

pawoSD · #8 03-05-2009, 05:00 PM

We all know how much effort it takes to push a button an extra time.

Does the seat have a pop up timer?

Rick76 · #9 03-05-2009, 05:14 PM

I'm old. My finger is worn out.

865sp300e · #10 03-05-2009, 05:29 PM

Quote:

Originally Posted by Rick76

I'm old. My finger is worn out.

and I bet you like the smell of frying bacon

babymog · #11 03-05-2009, 06:52 PM

You've got to own bun-warmers to understand I think. If I wanted it turned back to low, I'd turn it back to low. It reverts to low on its own, and on really cold days it's too soon.

I think this is a good mod, thanks again Rick.

Following your change, is it just as easy to defeat the timer circuit so that it never changes back to low?

pmckechnie · #12 03-07-2009, 10:13 AM

Rick
Is the control unit you modified from your 76 280? I looked in one from a junk 500SEL I have and it is a different number and has no resistors with the color code you mention. I was looking through Alldata and found that the wiring diagrams for the 82 and 93 S cars don't use a control unit, only a switch and 2 heaters per seat. 82 is as far back as I can go. It looks like with switches from a 82 or 83 and some wiring changes we can have manual heated seats as some others mentioned. This would suit me. Can you or anyone shed some light on this?

Rick76 · #13 03-07-2009, 02:51 PM

The module that I modified is from my wife's 89 260E.
Having a 126 part number, I would imagine that it was used in all vehicles of that vintage.
Looking at the 124 wiring diagrams, it looks like that module was used from 4/1987 to the end of production year 1990. Looks like my 95 E320 has a different module which I haven't bothered to modify cause I have a beater for winter and haven't got around to buying snow tires for the Benz. I will look into what needs to be done to modify it when I have some time.

Babymog, you might be able to get it to act manually like you want by removing that resistor entirely from the circuit (unsolder and lift one leg). I'll try it on a spare that I have and see what happens.

babymog · #14 03-07-2009, 06:17 PM

Mine are on the '94 and '95 so probably like your wagon Rick.

Thanks.