300D w123 climate control electrical problem - PeachParts Mercedes-Benz Forum

PerkHouse · #1 07-22-2013, 10:44 PM

As I mentioned in another post I'm having an electrical problem with my climate control.

The ignition switch was replaced last summer to resolve intermittent starting issues. I pulled the ignition switch wiring harness out today and squeezed the pins a bit just in case it was a loose connection, but that wasn't it. (It did resolve a long-standing issue with flickering dash lights though.)

I have also determined that all the other fuses are getting power from the ignition switch, but fuse 8 is not. If I temporarily jumper from any fuses over to 8, the climate control system functions properly.

Does anyone have an idea what may be the problem?

Thanks in advance!

PerkHouse · #2 07-23-2013, 07:27 AM

Oh, and the official Mercedes shop manual is absolutely useless. Whoever did the scanning of the photos and diagrams should be fired. I wish I had spent 1/3 the cost and bought the Haynes manual, but I thought that the OEM must have a superior product... bah!

funola · #3 07-23-2013, 09:24 AM

Per FSM, fuses 8, 6,10,14,12 are all hot in run and fed by the same rd/yl wire from the ign sw. Are you getting power to all 5 fuses in run? If not, could be a bad ign sw or the rd/yl wire connections.

PerkHouse · #4 07-23-2013, 10:01 AM

Yes, 6, 10, 12, and 14 are all hot in Run, but 8 is always dead on both sides of fuse. (Fuse verified good)

funola · #5 07-23-2013, 10:47 AM

Quote:

Originally Posted by PerkHouse

Yes, 6, 10, 12, and 14 are all hot in Run, but 8 is always dead on both sides of fuse. (Fuse verified good)

Pull fuse panel and check how fuse 8 is wired on supply side. Burned wire? Wire came off? Disconnect battery before work on fuse panel.

PerkHouse · #6 07-23-2013, 11:35 PM

Ok, I pulled it through the firewall (though I couldn't get it all the way out) but I couldn't see any loose/burnt connections... nothing visibly wrong.

This post claims that 15X (RD/YL) on the ignition switch goes to Fuse 8.

If that's true then maybe the problem is the (brand new) ignition switch.(?).

funola · #7 07-24-2013, 12:31 AM

My w/d shows F4,6,8,10,12 are connected together and fed by rd/yl wire in run. I can see on my fuse panel that F4 and 6 are connected by a copper bar (on fuse side of panel), same with F10 and 12, but F8 is by itself. So they must be connected together in the back somehow.

It is puzzling how you can have power on the other 4 fuses except 8 in run. You need to look at a w/d and verify the wiring.

PerkHouse · #8 07-25-2013, 12:57 PM

Ya, but the Mercedes FSM on CD is the worst I've ever seen - a total waste of money. (And I have 2 degrees and 20 years experience in electronics, so I'm pretty sure it's not me.)

However, if that post from Benzworld is correct, this might make sense. That post claims that fuse 4 (and 6?) are fed by 15R (gn/rd) and 15 (rd/bk) feeds fuse 12 (and 10?).

So, if that's true then perhaps the contacts in the ignition switch that connect power through 15X (rd/yl) to fuse 8 are defective.

I'm out of town right now, but when I get home, I'm gonna pull the ignition switch harness and check continuity from 15, 15R, and 15X to the respective fuses according to that post.

If it does turn out to be the ignition switch, I'll probably install a bypass relay and drive it from 15 or 15R rather than changing the switch again. It was just too much of a PITA to do it again in this lifetime.

PerkHouse · #9 07-31-2013, 10:51 AM

New info...

According to my (rather cheap) ammeter, the Climate circuit (fuse 8) is drawing about 17 amps, but not blowing the blue fuse. So assuming my meter is wrong, let's say the circuit is drawing 15 amps. Does anybody know what the normal draw is for blower on high and compressor clutch engaged?

What I'm wondering is if maybe there is excessive current being drawn causing the contacts in the ignition switch to fail.

funola · #10 07-31-2013, 11:08 AM

Quote:

Originally Posted by PerkHouse

New info...

According to my (rather cheap) ammeter, the Climate circuit (fuse 8) is drawing about 17 amps, but not blowing the blue fuse. So assuming my meter is wrong, let's say the circuit is drawing 15 amps. Does anybody know what the normal draw is for blower on high and compressor clutch engaged?

What I'm wondering is if maybe there is excessive current being drawn causing the contacts in the ignition switch to fail.

Your amp numbers are correct. I measured my blower on high a few years ago and it was around 16 amps. I changed F8 to 25 amps and no more problems with fuse blowing.

Unless the FSM is wrong, I don't see how it can be a failed ign sw since you are getting power to 3 of the 4 fuses.

funola · #11 07-31-2013, 11:13 AM

As I recall, red is 16 amps. Blue is 25?

PerkHouse · #12 07-28-2014, 10:48 AM

Well, the saga continues...

I made a jumper to connect the hot side of Fuse 8 to the RD/YL wires and the AC worked for maybe 2 days. (It worked great too!) But then it burned out the ignition switch. Fortunately, I had saved the old one from last year. I removed the jumper, disassembled the old switch and verified all of its contacts were good, then replaced the burnt one with the old one. The car starts and runs again, but now it's back to no climate control. What a PITA!

Edit: And I only have today and tomorrow to solve this before I go back to work (this time in Angola) so if I don't solve it quickly, my daughter is gonna have to go through another NC winter with no heat until I can get here next July.

funola · #13 07-28-2014, 11:16 AM

Quote:

Originally Posted by PerkHouse

Well, the saga continues...

I made a jumper to connect the hot side of Fuse 8 to the RD/YL wires and the AC worked for maybe 2 days. (It worked great too!) But then it burned out the ignition switch. Fortunately, I had saved the old one from last year. I removed the jumper, disassembled the old switch and verified all of its contacts were good, then replaced the burnt one with the old one. The car starts and runs again, but now it's back to no climate control. What a PITA!

Edit: And I only have today and tomorrow to solve this before I go back to work (this time in Angola) so if I don't solve it quickly, my daughter is gonna have to go through another NC winter with no heat until I can get here next July.

When you say no climate control, do you mean no blower or no ac compressor pulling in or both? If blower only, you may want to take a look at this post http://www.peachparts.com/shopforum/diesel-discussion/357857-cabin-blower-stopped-fixed-w-photos.html

At this point it may be less work to run new wires with a new relay to the blower instead of trying to fix the factory wiring, which is not an easy task to do properly.

PerkHouse · #14 07-28-2014, 12:36 PM

Quote:

Originally Posted by funola

When you say no climate control, do you mean no blower or no ac compressor pulling in or both? ...

Neither works when it's in the fail state. I had the same thought you did and bought a 40A automotive relay from Radio Shat in case I needed to re-wire, but I honestly don't think I have time for that either.

Here's the irony... I just got it all put together with the new (old) switch and when I started it up, the climate control is working. (Did I mention the problem is intermittent?)

Thanks for all your help Funola!