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Heater Blower Constantly On.

Started by calvin streeting, 07 October 2010, 08:14 PM

calvin streeting

Ok. I had a dead heater (more of a fuse blower :) ), so i replaced it with a working version.. and all fine. but then yesterday it turned its self on (full blast). and not off.

being lothed to take out hole heater again, I removed the connector on the back of the control switch (on dash), and it still ran.

so I looked at the circuit diagram (emailed to me from classic.center@daimler.com This e-mail address is being protected from spambots. You need JavaScript enabled to view it ) very helpfull and found that there seams to be a circuit that bypasses the resistor bank.red wire



so to confirm this i removed the wire from the connector on the firewall and hey presto the fan shut up. but still works when i ask it

so whats it connected to ? looking at my spare (photo later) it seams to be a bimatlic strip.

so whats it for?

calvin

sannerud

#1
Hey.
Can't see the function of this bypass, but maybe someone else know... If I understand you right the fan work at all speeds when you use the control switch on the dash and the bypass is disconnected?? If this is correct my suggestion is to leave it that way. But if not, it sounds like it's your pre-resistance/resistorbank that needs to be replaced. Take a look at this post and you you'll might find out some more :)
http://forum.w116.org/mechanicals/'78-280sel-rhd-(uk)-heater-problem-1/msg72905/#msg72905  
(I've checked the Mercedes-EPC and the correct partnumber for the resistorbank is: A 116 835 01 06)

koan

The idea is if the fan resistor bank overheats the bimetallic strip contacts close shorting out the resistors. The resistors cool down with the fan on full speed.

Replace the resistor bank or, if it can be opened up examine why the shorting contacts are closed.

koan
Boogity, Boogity, Boogity, Amen!

sannerud

There you go! Nice to have some real experts here :)

calvin streeting

thanks.. I will stick my arm backup inside the depths of car and fish it out. might tie some string to first so it's easyer to pull new on through.

one thought on the bimatlic strip is that my spare one is sitting in the closed posistion, where as the wiring diagram shows it open in default state. so i asume my spare is also dead :( ..

now to hunt down a new one (in UK).

calvin

koan

Maybe the contacts have arced too much and stuck together, separating them with a knife blade and cleaning them might work.

If both have been in the car and both have ended up in the same state there could be something amiss elsewhere.

koan
Boogity, Boogity, Boogity, Amen!

peterq

Just been through this on my 450SLC. Same symptoms, and the cause is the bimetallic strip. Its meant to handle overheating in the resistor box. In my case it was coming on as soon as the ignition was switched on even though the temperature outside was at 0 and the fan was actually switched off. I pulled the wire from the box, nothing's caught fire so far.

calvin streeting

i took my other one and noticed the bimatlic was closed.



so i bent it back open and did some tests using a solder iron, and it closed



and let go to see if it returns.



Ok defenatly a tempover load.. but maybe it can be fixed... but not quie sure how much of a fire hazarad it would be  :-\

but maybe this can be done with the heater in place through the hole (carfully)..

calvin