w115 Heater Fan issues

[Jake]

1976 w115 300D .

Heater / A/c fan system has stopped .

There were a couple of times is was sketchy on start up , then just no go.

No previous noises from the fan.

I was imagining mortgaging my soul to buy a new heater fan , then I discovered , there is another fan for the AC , and some interaction between the two and the switching stuff .

All very confusing for me .

What I want to ask is, what do I test , and how , and where .

All thoughts gratefully received .

[Bartman4800]

First things first.

Have a look at your fusebox

Replace all aluminium fuses with the correct copper fuses. They are know to corrode (galvanic corrosion due to dissimilar metals)
Clean up the fuse terminals with a bit of scotchbrite cloth.

If you are sure the fuses are all ok, you can look onwards.


Bart

[Jake]

Thanks for your suggestion Bart , yes , the fuses all appear good , I did replace them with brass about 10yrs ago when I woke it up from its pre purchase 12yr slumber party . But I have rechecked them again today.

So I fluffed around with a meter today , not really knowing what I was looking at , but I found it interesting that the 2 wires that connect on the insulated junction box on the compressor , have no resistance to earth ?

I have also found a couple of heater fans in the shed, that have resistor boxes attached , both fans work on 12v , but neither box works thru the resistors ? one box has both contacts open , the other box has both contacts closed . Something odd is presented here .

[Tony From West Oz]

Thanks for your suggestion Bart , yes , the fuses all appear good , I did replace them with brass about 10yrs ago when I woke it up from its pre purchase 12yr slumber party . But I have rechecked them again today.

So I fluffed around with a meter today , not really knowing what I was looking at , but I found it interesting that the 2 wires that connect on the insulated junction box on the compressor , have no resistance to earth ?

I have also found a couple of heater fans in the shed, that have resistor boxes attached , both fans work on 12v , but neither box works thru the resistors ? one box has both contacts open , the other box has both contacts closed . Something odd is presented here .

Are you saying that the resistance is 0 ohms or infinite resistance?

[Jake]

No resistance , like a direct short , zero ohms .

[Jake]

After following some suggestions of what to look at , without dismantling the car , I spent some time laying on my back , under the dash today .

I fiddled with the green knob and watched the vacuum pod move the rod .

Near by , kinda laying against the steering column , was a device , plugged into the loom , that had a very strange looking curved piece of thin metal attached. It was odd , as it didn't seem to have a function there .

I wondered if it was part of the cruise control stuff ........ but it seemed odd just hanging there .

So I pushed on the curved lever part AND THE FAN STARTED TO RUN. ...................

Then I figured that it was supposed to be attached to the side of the heater duct box . The two hollow brass rivets had sheared the tails off leaving it hanging by the loom.
I fixed it by replacing the rivets with some 3mm x 50mm screws and remounted the device where is was supposed to be .
Now , when the green knob is rotated , the vac pod pulls the lever , actuating the switch and the fan runs , blowing air out the top vents .

This is the aux fan blowing .

Adjusting the heater fan control , it works thru the 3 speeds as desired .

This will give me cold air just as soon as I get an R12 top up . (I checked the service date on the dryer , for when I replaced it and found it was 10yrs ago, time flys when you're having fun) . So I hope to get that sorted this week.

DSCF2128.JPG

DSCF2136.JPG

DSCF2133.JPG

[Jake]

I would still like to know if the contacts in the heater fan resistor box should be normally closed or normally open (with no power applied) .

[Jake]

Initial attempt to top up the gas was unsuccessful, there seemed to be a blockage in the system preventing flow .

I found the expansion valve (under the glove box) and pulled that out , found the wee brass mesh filter was blocked , cleaned that out , refitted the unit , more gas :) :)

COLD AIR , whoo hoo ,, first time in years . LOL , I really should stop procrastinating when things get a bit tricky .

[Tony From West Oz]

Congratulations!

When dealing with the unknown, it is better to procrastinate a bit while you research the issues, then have a good look at the area were the issue is causing impact. ask for help (someone else may have done it already).
Then you can start cautiously investigating further.
Once you start pulling things apart it can cause the problem to get worse.

Now you have posted the remedy for your problem, someone else (who needs this information in the future) can search and learn the solution that worked for you.

[scraf]

Just a random comment, in the Netherlands you must have a working fan to get through one's technical check. Mine's not working, have a replacement, but reading through the replacement instructions is more than scary. First step remove seats, followed by 30 other pages, including " remove dashboard, see attachment, another 16 pages ". ( might be confusing the procedure with that if a W116, as it goes ).

At the end of the day, one can go to the dollar store and buy a 12 volt fan and gaffer tape it to the dash. Fan ? Check. Working ? Check. Pass technical, er, check.

[Mercmad]

To replace the fan in any of w114 and W115 's is a LOOOOOONG job. I start with removing the seats, then the console, followed by the steering wheel then the windscreen, followed by the dash. yes a very long job and by the time the you have bought a good fan, restored the dash pad, and console, replaced the screen and rubber you will have spent a fortune.