This dang Bio diesel is causing problems! I know alot of you guys have much more wrenching old mercedes experience than I do. So I thought you may be willing to help. I've had the 79, 300SD parked for about a month and got in started it up, warmed the engine and have no heat, burrr. Depressing the defrost, auto high and low switches at the panel do nothing, no fan running. I then turned the key to the off position and it tried briefly to stop but not enough vacuum. Every time I have tried to shut it off with the key since then it doesn't even attempt to shut off. Also the door locks make a vague attempt to lock but the engine doesn't even attempt to shut down now. I just replaced a couple broken vacuum lines in one door and under the hood as well as replaced the X and Y chineese fingers and check valves under the hood last summer (even then with the couple broken lines the heat worked fine). That took care of the shut off problem last time so I know I have a vacuum leak somewhere that I need to find. I checked the vacuum pump, it's pulling good, 25 what evers are on the gauge. Could a broken vacuum line cause the fan not to run? Or do I need to look for a vacuum leak and an electrical issue? It's cold sitting in the car this time of year much less working on it in the cold.
Thanks
-Dave-

You don't have problems with biodiesel. It sounds like you've either got a big vacuum leak or a bad vacuum pump. It will take a methodical approach to identify the cause. Plug all connections near the pump and check for vacuum at the pump. If your pump is good, reconnect all the plugged lines one at a time and monitor for vacuum drop. When you get one, chase it down and fix it. I've had lots of problems with aging door lock actuators.

I've never worked on the climate control system, but lots of things to go wrong there too.

Thanks UFO,
I know it's not boidiesel related. That was my attempt at a little humor. I checked the vac at the pump. It's good. I also checked the vac line going into the back of the fuel pump that kills the fuel supply, it's working as well. I'm trying to avoid the methodical elimination route. Call me lazy.

double d!
the vacuum lines must have come off at the switch or the switch part is bad. PUll out the dash and look down and feel next to the switch for the 2 brown lines with rubber connectors on them., they need ot both be connect to the switch.
also I would plug the vacuum to the windows by the oil filter. they are the 2 yellow plastic hoses. take out the yellow connectors and plug the one hose coming in.

The vacuum leak's not at the switch. I've bypassed the X & Y connectors that the vac pump line runs into and connected the line from the vac pump to the brown vac line that goes to the switch and it works (shuts off the engine but still no heat) flawlessly.

MB help here is where I have gotten a lot of info for my MBs 86 300SDL and 80 300SD. And maybe you already found the site.

Thanks Grubby,
I'll give them a shot.

Here is a DIY vacuum guide I wrote up on another forum. It may help you track down your vac leaks.
DIY Vac Troubleshooting Guide at Schuman's Auto

quote:

Originally posted by biodiesel300TD:
Here is a DIY vacuum guide I wrote up on another forum. It may help you track down your vac leaks.
DIY Vac Troubleshooting Guide at Schuman's Auto

That site won't let me in. It keeps saying "Sorry, registration has been disabled by the administrator"

Oops I forgot, the admin is doing a bunch of restructuring of the forum. So new registration is disabled for a while. Please be patient, we're trying to deal with Spammers mostly. But you should still be able to view everything you just won't get to see the photos.

my fan, air circulation, and radio is intermittent as well. Chalk another one up for the to do list.

quote:

electrical issue?

Hi Double D, I think you got an electrical problem with the motor not shutting off, it's probably in the ignition switch.

You have a shut off valve that has likely gone bad. Not uncommon. www.mercedesshop.com is a great forum that I use and have saved hundeds of dollars based on repair information and diy advice.

Double D,
It sounds to me like you have several issues, not just one. First, the climate control servo is probably bad. I have a 80 300SD and just had to replace mine. It is the "Box" looking thing with wires coming out of it, behind the air cleaner(Almost touches it). When this goes bad, it will screw up the ACC(automatic climate control), and in turn sporadically give out heat or nothing at all. There is also a ACC amplifier that also goes bad behind the glove box. They are all over ebay for under $70. I knew mine was bad, because when I would tap(hard)on it with a screwdriver it would temporarialy work. These parts(the servo) had EXTREMELY HIGH FAILURE RATES, right out of the box. You can get a new rebuilt one as I did, or now they have digital ones, in which Im not as familiar with. I would almost, and again I say almost, as I may be wrong, that the servo is bad. Way to check is look around the housing for leaks of coolant and when it is suppose to be running it should vibrate a little and should be able to hear gears and grinding. I had the exact symptoms in reference to the acc. replaced it and the amplifier! Bingo! Probelm solved! At least for me.LOL

As for the engine not shutting off, there is a shut off valve built into the top of the IP. Check for all vaccuum leaks first, as this part is usually $100.00+. Remember to check the vaccuum lines in the trunk as well. I currently have vaccuum issues myself. I have already tore the door panel off. I suspect that it is the central locking mechanism. These are usually the culprit. Spray ether or WD (sparingly) around the vaccuum connecters and listen/look for succking sound or bubbles. Hope this helps. Email me with any questions, anytime. I will help if i can.

Thanks for the reply's guys,
I had temporarily bypassed the vacuum system by just routing the vacuum to the switch and the switch to the IP shut off. At least then I could shut it off without having to open the hood. Since it's warming up now, I haven't been too concerned with the heat issue. Yeah the servo has been shot for a long while it's just set up for heat no AC wich I'm OK with. Maybe I'll get to take it apart one day.

I have a '79 300D and have had it since it was new. I have experienced similar problems. The climate control unit under the hood operates both electrical and vacuum systems and is quite complex. One easy problem to eliminate regarding lack of heat is to check the fuse box for blown fuse. I went one winter without because of this simple problem.

As for the vacuum leak, it could be at a number of places. The bundle of hoses pass through the firewall behind the battery box. My experience has been that they become brittle because of the battery acid fumes and can break easily. Check there first.

Hope this may be of help.

Gabriel