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'78 280SEL RHD (UK) - heater problem #1

Started by joshm, 25 April 2010, 04:48 AM


Is this climate control or 2 knob A/C?

I could be wrong but I seem to remember with 2 knob A/C the resistor module is on the inside attached to the HVAC box near the motor so the resistor elements are in the air flow.

If the blower is running flat out it suggests the resistor module is getting too hot. It has a bimetal strip thermal circuit "maker" that connects the blower to the high speed contact regardless of knob position when over heating.

Module getting too hot is either stuffed module or insufficient air flow, fan clogged with dirt for instance.
Boogity, Boogity, Boogity, Amen!


Hey koan ... thanks for steppin' up and helpin' out ...

No, not climate control or 2 knob AC ... pic of my controls attached ...

I appreciate the explanation of the bimetal strip ... this gives me a better appreciation of what's happening, because, the fan (speed control) behaves when cold and will later come on full speed all by itself after the car is run for any distance ... the air flow / dirt clogging of fan is a distinct possibility in my case ... lots of seasonal tree debris, ect.

So ... should I be able to disconnect the S.R. module wiring harness on the engine side of the firewall and direct high pressure air into / around that module / fan?  And then dress up the contacts with DeoxIT D5 ... as I mentioned I'd thought of doing earlier ... ?

I just don't want to break the connector ('73 280SEL German domestic production model 116 025 ... everything's old and wants to break) trying to get it apart without understanding it fully in advance.

Thanks, FFF


Hmmm... One knob heat... don't see many of them.

Had a look at the book and my car to confirm, the blower resistor plug is on the fire wall in the engine compartment.

First off I'd liberally spray WD40 or similar on the connector where the parts meet and then try to wriggle the connector off by hand. Next stage would be to try a thin trim removal tool where the parts meet. I wouldn't try a screwdriver blade (yet), I've cracked a couple of brittle connectors over the years. Finally I'd try to get the cover off the connector (pops off the top) and then remove individual wires with long nose pliers and WD40 noting wire colour codes and positions.

On the car there are screws next to the connector, removing them might allow the resistor assembly to be removed with the plug connected.
Boogity, Boogity, Boogity, Amen!


Hey koan ... thanks for steppin' up and helpin' out again ...

If I can't remove the resistor assembly with plug connected through the opening from the engine side of the firewall (doesn't sound like joshm or sannerud had any luck with that approach, or I'm sure they would have done it instead of from the passenger side ... which sounded like an ordeal ... see 25 April 2010, 06:20 AM & 25 April 2010, 01:33 PM posts, below), what do you think of my idea to force high pressure air into the opening (all around, to the extent that there is an air gap available) to try and dislodge accumulated dirt from the assembly and restore normalized temperature operation of the bimetal strip?  Followed by treatment of all of the electrical contacts with DeoxIT D5 and re-assembly?

I appreciate the advice on use of WD40 and incremental use of thin edge-type tools to get the connector apart ... I'll pick a dry day and start early ... with all due care and patience ... today ain't lookin' like that day ... wet west coast weather prevails here in Vancouver, Canada ...



Thanks for a great thread. im stuck with a fan on full speed. dont seem to reach it from inside of the blower motor hole. but ill try some more until i can reach it. is it straight up or up to the left? the cables seem to disapear to the left. but when i look at the schematic it looks different. how did it turn out for you others out there?


Henrik.H ... glad you found joshm's thread useful ... I picked it up again on 12DEC14 and koan's been helping me figure certain stuff out ...

... to be honest, I have not made any progress up here in the great white north of Canada, as I have to work on stuff outside and its' been crappy weather, then Xmas, then more crappy weather ...

... not that I have any intentions of trying to go after the resistor assembly from inside the car (sounds like a clusterf&*k to me, a big guy with big hands and a bad back), nor have I tried my high pressure air idea yet (high hopes tho) ... I had to pull the blower fan fuse the other day as the car was getting to a low voltage state at idle with everything running (lights, wipers and that damn fan) and then stalling on me ... I'll report back to this thread once I've made some definitive progress ... FFF


Hi again.

i took out the resister assembly and cleaned it (it was quite rusty nasty looking) and then put it back into the hole up to the left. and then i took a flashlight and looked in the hole from the engine side and there i could see it, i just lifted it up with a screwdriver and then grabbed it with a plyer and put the screws back. it wasnt too hard. but trying from inside the blower tunnel it would be almost impossible. the sad part is that it worked one time then it got stuck in fast mode again. so i went to the scrap yard and found another unit. ill take it apart and clean it and then change it out. ill let you know how it works out.  :P


adding to my post that the weather here in sweden is cold and nasty as well. no good weather to try out the new 280s in ill try to get it rolling as soon as the weather is a bit nicer. i bought a black refinished 75. it had been in a garage since 99. and all the carpets and interior was in the trunk. im putting everything back bit by bit.sloooow process everything is loose or missing. anyone sitting on the 4 sticks for changing heater and air flow on euro model. ill be interested of buying them.  good luck all.  :)



Enter this into eBay Australia:  w116-mercedes-benz-23-X-interior-parts-Bulk

Someone in Tasmania is selling a bucket load of 116 interior bits.

Good luck.
Sydney, Australia


Thanks  :) a lot of good stuff but all i allready have exept the four sticks  :P only ships to Australia as well. Till keep on löpning for ththem bit IF you ser something till apreciate it. Cheers.