My 1987 300d has a clicking noise behind the push buttons sometimes and the blower will cycle on and off rapidly.Most of the time the blower won't come on at all,and I don't have power at the fusible link(both sides)unless the blower does come on.I thought it was a supply problem so I replaced the ignition switch with an OEM,but still have the problem.When it was running at one time I pulled out the push buttons the noise is not coming from them.The noise is definitely coming for behind and not on the right side kick panel.It seems like it works normal if the car has been running a long time,about an hour even the motor sound good with the control varying the speed the way it should,Im stumped.All help is appreciated,it's getting colder outside.Merry Christmas to all

I had the same problem, the fault I believe lies in the push button control unit, could be cold solder points. I swapped mine out with one from a pick and pull, no more clicking

I don't know what can click in the ACC controls but the solenoid bank also back there that directs vacuum (so to speak) to the various duct actuators in the dash makes a click sound when changing modes. The solenoids rarely go bad so the problem is likely in the control unit sending strange signals. Wait, didn't the previous post just say that?

Sixto
83 300SD

You definitely have a problem with your blower supply. You should have 12 volts on the 30 amp strip fuse whenever the ignition switch is in the Run position. Power comes off of a separate set of contacts (terminal 15X) in the ignition switch to supply power to the fuse and then on to the blower control module. Use your voltmeter to trace back from the fuse to the ignition switch. Was the ignition switch that you changed new or used? Just the electrical section or the whole assembly?
Also try wiggling the key. Sometimes the mechanism wears or gets gummy and the switch doesn't fully return to the Run position to engage the blower contacts. Cold weather makes it worse.

The ignition was a new Mercedes part and it was the switch only,like you I think it's a power supply problem I just don't know the path,all the schematics I've seen were too blurry and were no help.I just need to know the path from the ignition switch to the fusible link,I think that's where the problem is.Also note besides not having power at the fusible link,if I run a hot wire to the link nothing works,it's only sometimes after hearing clicking behind the push buttons the blower will start and all functions work normal.Thanks for your reply

This thread opens with a blower controller diagram. Still looking for power distribution. For kicks, route power directly from the battery to the ACC fuse. If the symptoms ease, it could be the key switch. If not, more likely the PBU.

Sixto
83 300SD

Here's an '88 Euro gasser power distribution diagram which shouldn't be too different from an '87 Diesel -



IIRC ACC is fuse 5, blower is fuse 16 onboard or 30-amp external.

Sixto
83 300SD

From the 15X terminal on the ignition switch there is a heavy pink/green wire that goes to fuse 12 socket. Another pink/green wire comes off the same terminal to the strip fuse. From the other side of the strip fuse is a black/green wire that goes to fuse 12 socket and then on to the X16 three way connector on firewall above brake booster and then on to the blower speed controller (underneath blower motor).
Note that there should be no fuse in position 12, it is only used as a tie point to hook in the strip fuse wiring. This is only for MY86 and 87 as the strip fuse addition was a modification from the original F12 setup. Look for loose screws at F12 and the strip fuse holder.

Sounds like you have 2 problems if feeding directly to the strip fuse does not get your blower going. I don't know what would be the source of the clicking unless it is the solenoid pack for the vacuum actuators. As others have stated, that could be caused by the pushbutton unit. Bad solder connections are common.

I ran continuity from 15x to fusible link and that proved good,I then put a jumper between 15x and 30 on the ignition plug and had power to fusible link but still no blower,I also checked continuity on the ignition switch between 15x and 30 and it checked good,doesn't make any sense,I did take the push buttons apart and checked carefully and all solder joints looked fine,I'm stumped

Problem 1 - Blower motor supply intermittent:
Check screws holding the strip fuse to check if tight.
Disconnect battery negative. Remove fuse and relay center cover (6 screws). Remove 1 screw front center of fuse assembly and lift assembly up. Check tightness of screws on fuse 12. Check the wiring going to that fuse. The modification for the external fuse would have been done at the dealer so check that work.
Does the connector on the ignition switch have soldered terminals or screwed on connections? I don't remember. If screws check for tightness.

Problem 2 - Intermittent acc function.
Check all fuses related to the acc for cracks that are not always visible.
Pull the pushbutton unit and remove the bottom cover. If it is a MK brand, check for bad solder connections (cracks). Pay particular attention to where the temperature potentiometer connects as well as the pushbutton switches.
If it is a Bosch, check for signs of overheating around the center of the board and cracked solder connections in that area.

After I replaced the ignition switch I now have power at the fusible link but still no blower so I ran wires to the plug that feeds the blower and it now runs.Am I to assume the climate control button unit is the problem now?And let me take a second to thank all you guys on this forum that have me advise that got me in right direction

If you mean the blower junction above the brake booster, there isn't anything but wire between the climate control unit and that junction. There's still the possibility you're not getting solid power to the control unit. Maybe run a wire from the kick panel distribution center to the control unit to test.

I have a control unit Jeremy tested as good years ago. I don't know exactly what car it's from but I got it as a spare when I bought his '87 300D. Yours for the cost of shipping.

Sixto
83 300SD

Sounds good to me I'll do that let me know how we can do the transaction or call 518-821-3542 Thanks Lou

Lou Torelli 470 Kings Highway Saugerties New York 12477 Just let me know what I owe you,Can't wait it's cold here Thanks for your help

I received the parts you sent last night and installed it this morning.Thanks to you I have heat again.Now I can tinker with some other little things on the car to get in as good as shape I can.I put a check in the mail,let me know when you get it and thanks to you again and all the others that gave some help on this project. Lou