Please direct me to possible causes/fixes for this issue.

They seem to randomly- stop working (at the same time)... then Tach works/and AC starts again.

I read Klima relay is one suspect.

what are the others?

thx

OVP relay. The Tach pulse comes from the EDS computer. When the OVP goes crappy, you lose the EDS computer (and the tach pulse it puts out), the electronically controlled idle, and ABS system. The Klima receives the tach input from the EDS computer, if it sees no tach pulse, no A/C and no transmission kickdown.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I all ready replaced the OVP RELAY

I still have the problem... so does that mean a glitch in the EDS? Or the Klima?

Of course-- it could be a weak/bad connection with the New OVP connection.

Where should I start ??

You did help me figure one other issue I have. It seems like the car shifts w/ clunk from time time- when accelerating on turns... I was worried it was differential issue... BUT-- it was gone for a while- came back yesterday- BUT at same time the Tach stopped working... so as YOU mentioned above- NO KICKDOWN is the issue (not the diff)...

does that point to the Klima- not seeing signals???

The KLIMA relay is a slave device, it responds to the Tach signal, it does not generate it. Loss of tach pulse is a result of loss of signal from the EDS computer. This can be a power issue (crappy fuses in the fuse box) or a crappy OVP. If the OVP is anything other than a brand new unit from the MB dealership, hit the trash with it and shell out for a good one. They're a known problematic device that fails with age and the aftermarket ones are 100% garbage. Check charging voltage as well, if the voltage regulator on the alternator is bad, it's possible that you could be overcharging and the OVP is actually doing its job.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

How does one check charging voltage on alternator voltage regulator?

Same as any other car. Digital voltmeter across your battery leads with engine running. You should be 13.5-14.4V. Have a helper rev the engine to ~3000 RPM and check again. Voltage should be no higher than 14.4V. If its too high, the regulator is bad. If it's too low, the regulator can be bad or the brushes worn out.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Thanks- I will do that today...

Re- Intermittent losses Tach/AC - at same time

I texted with Pierre Hedary (MB guru in Florida) and HE said it points to the Klima. so I am a little confused ...

Does it make sense to Pull the OVP and test off of 12V source (seen video from Diesel Mercedes (youtube)) to see if it is working correctly?

I don't care what Pierre Hedary (MB guru in Florida) said, AC loss by itself can be Klima. Losing the tach is not. The Klima uses the tach pulse from the ECU to determine if the engine is running and whether to engage the compressor. No tach pulse from ECU means no tach gauge and no A/C or Kickdown. It's just that simple.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I tested the Voltage w/ Idle (13.6) and with helper- running 3000 rpms- held steady 13.6-13.7volts

so Alternator voltage good!

Tach - stopped again today... spoke w/ Indy MB mechanic (never worked with)... he suggested short or capacitor in Inst. cluster?

so-- when tach was not working today-- I gave it a quick slap on top of dash... and Tach jumped back to life again!!!

Pulled in garage tonite-- turned head lites off... and tach bounced down a little.

Do these last 2 symptoms/signs-- point to anything??? Gotta be wire/connection in cluster--right?

Just keep banging on dash. It happens with my SDL sometimes, never bother me. I have a spare SDL dash if you are interested.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Do You also lose AC -- when the Tach stops working?

The tach doesn't bother me... the loss of AC - would though on hot day!

The tach does not generate the Tach pulse, nor does the Klima relay. They originate from the EDS computer. Losing both at the same time means a common source - EDS computer or crappy connection somewhere. Your striking the dash could mean there's a bad connection somewhere or enough of a shock to jostle the OVP relay on the firewall.


Until you decide to do some actual troubleshooting instead of asking questions constantly and trying nothing suggested, you will continue to have problems with no resolution.


Let us know when you fix it.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I will test the OVP relay- as Diesel Mercedes - video on Youtube demonstrates... if that works correctly-

if I follow you correctly-- I would assume- Tach/wire issue- then EDS sends no signal to Klima-- then NO AC

correct?