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#1

Mechanicals / Weird AC Clutch Voltage Drop?

Last post by aaronec91 - 28 April 2024, 09:34 PM

Hi all! Recently acquired a 1979 300SD, runs great and been using it for a couple weeks as a commuter, my first diesel Mercedes! A PO had repaired the AC system (new compressor, upgraded/rebuilt vacuum servo, R134). To clarify this is the auto system with the big temp wheel and push buttons. The system worked flawlessly until yesterday...everything still functioned, except no cold air or compressor engagement.

Ran through some tests, jumped the comp clutch to 12v and checked pressures (about 40/150 when running) and when jumped the system works, blows cold. Probed the unplugged clutch electrical connector with engine on and climate on, get full 12v. However, I backprobed the clutch connector, and as soon as I plug it into the AC compressor, voltage drops to 0 (between 0-0.01 on my meter) and clutch does not engage, unplug it and full 12v again immediately. I also checked the AC On/Off dash switch and it gets power and seems to have continuity where it should.

I would expect if I have a shorting AC clutch, my leads would get hot and/or it just wouldn't work, or fried something else, preventing any voltage from appearing, but unplugged there's 12v to the clutch connector. Looked at the wiring diagram from w116.org and it doesn't appear the clutch is controlled by the climate amplifier, just a series of switches. I'd think if any of the switches were faulty it would get no power.  Am I missing something here?? Thanks!

#2

Mechanicals / Re: Dome Light Delay (1979 300...

Last post by kjenkins - 28 April 2024, 02:14 PM

My 1979 300sd has no delay.

#3

Mechanicals / Re: Dome Light Delay (1979 300...

Last post by rumb - 28 April 2024, 12:11 PM

https://handbook.w116.org/ETM/

The wiring diagram for om617 does not show the delay relay.

#4

Mechanicals / Re: Dome Light Delay (1979 300...

Last post by benzjag - 27 April 2024, 08:12 PM

Any 1978-1980 300SD owners out there? Does your interior dome light stay on for a few seconds after closing the front doors?

#5

Mechanicals / Re: 1976 450SE fuel fitting.

Last post by Labninja - 26 April 2024, 04:34 PM

Thanks, I don't want to  have to do it over so I'll just get the right one.

#6

Mechanicals / Re: 1976 450SE fuel fitting.

Last post by Max-NL - 26 April 2024, 04:04 PM

As your car is from 1976, you should have the K-Jetronic system which uses the following hose : A1234700875 . Should be around $30 from the dealer. Or from FCP Euro or Autohaus:

https://www.autohausaz.com/pn/1234700875OE
https://www.fcpeuro.com/products/mercedes-fuel-tank-exit-hose-1234700875

#7

Mechanicals / Re: 1976 450SE fuel fitting.

Last post by rumb - 26 April 2024, 04:02 PM

You will want to use the hose with fitting:


https://www.ebay.com/itm/364569736448?mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=5338678874&toolid=20006%26customid%3Ds%253AGS%253Bgc%253Ae33c10a04233143f49b1768c56fffd16%253Bpt%253A1%253Bchoc%253A1&customid=s%3AGS%3Bgc%3Ae33c10a04233143f49b1768c56fffd16%3Bpt%3A1%3Bchoc%3A2&msclkid=e33c10a04233143f49b1768c56fffd16


Normally we would say Mercedes only, but several here have suffered early failure of thecloth covered hose from mb.  The cohline one above I would think a better choice.

#8

Mechanicals / Re: 1976 450SE fuel fitting.

Last post by Labninja - 26 April 2024, 02:56 PM

That would be 584. I replaced the pump filter accumulator and all tubing up to the hard line. I have a hose for part 584 but there's no fitting but,  the one I bought is NPT. I just wanted to be sure to get the right thing this time. Or is it easier to find the actual:"FUEL HOSE" ?





584    FUEL HOSE    001    A 11 647 015 75    -    $28.28
SEE FIG. NO.:
FUEL HOSE
Replaced by: A  123 470 08 75    -    A 11 647 023 75    -    -

#9

Mechanicals / Re: 1976 450SE fuel fitting.

Last post by rumb - 26 April 2024, 01:53 PM

Are you referring to the filter and/or the hose that goes into it?

What part on this diagram?
https://nemigaparts.com/cat_spares/epc/mercedes/1/fg/116032/68n/47/001/

#10

Mechanicals / 1976 450SE fuel fitting.

Last post by Labninja - 26 April 2024, 01:26 PM

Can someone tell me what size/thread type I need to look to replace the fitting that screws into the bottom of the fuel tank? I bought a stainless barb but the original is not pipe thread apparently.  It looks more like a hydraulic fitting. What do I need to look for?

Thanks,