Where is the EDS computer located?

On the 190D its right next to the Klima, behind the battery and the battery cover semi under the windshield.

So in order for the 2 relay bypass to work you still need the EDS to be working in good order??

I have no pin 4 so what would be the alternative place for me?

I could care less about any protection crap - engine overheating, compressor seizing - let the damn thing burn - as long as I have my A/C working!

Exactly wrong. If the EDS ISN"T working correctly, you can use the relays to bypass protection. If the EDS was working correctly, you probably wouldn't be doing this. Why are you doing this, by the way?

You have no pin 4, so all you need to connect is Pin 12, that's the only sense lead.

Here's the relevant diagram. After this, I start charging for engineering:

The heater core and receiver dryer was leaking so I dove in and decided to fix up the old girl ALL the way.
Replaced:
Heater core and Evaporator.
All vacuum elements ( except for the defrost one - out of stock worldwide- and still works )
Feedback potentiometer
New style switching valve.
Pushbuttons
Klima relay
Receiver dryer with both switches.

To the best of my ability I did all the tests to this system by the Tempmatic book.

Tried second pushbuttons and klima relay.
Grounding one wire of the low pressure switch does kick on the A/C compressor. Same with jumping pins 5 & 7.

"Help me Obi Wan Kenobi you're my only hope"

Damn...... nothing, no effect. Did not work :(

This is your key. According to the electrical print posted by Frank in Post 49, the pressure switch is beyond the Klima relay. If grounding it turns on the compressor, you have no refrigerant in the system (you have tested the pressure right?), the pressure switch itself is bad (test for continuity across the terminals), you have a fault in the pushbutton unit or the "Electrical center" shown in the print, or you have a wiring fault somewhere.

Test for basics first, make sure there is refrigerant in the system and you have adequate standing pressure. If you do, test for continuity through the pressure switch. If those things are good, you have a problem further downstream. It isn't the Klima.

I know/ tested the A/C charge is good, switch is good.
Please expand on " further downstream"
Would it be where the wiring goes in and out of the Electrical center/fuel box, continuity tests or yet another push buttons.
I'm all ears. And a MAJOR THANK YOU ALL for your input on this!

Study the diagram in Post 49. Pay attention to where the wiring goes beyond the pressure switch. The diagram shows wire colors and connector pin numbers. You need to follow it all the way back to the Pushbutton Unit. You should be able to test the whole system by grounding Pin 6 (blue/green) on the X1 connector on the PBU. If the clutch engages, the PBU is the problem. If it doesn't, somewhere between the pressure switch and the PBU you have an open connection.

I have no idea what the "F1 Electrical Center" is, but if it's anything like other electronic "modules" of the era, I'd be willing to be you have broken/cracked solder joints.

The PBU grounds Pin 10 of the Klima relay through the pressure switch to engage the compressor clutch. Since you can ground the circuit manually at the pressure switch, you've ruled out the Klima relay and the wiring up to the pressure switch. Now you need to prove the circuit the rest of the way back to the PBU.

I'm checking this out!

OKAY! So..... just like you said I found the pin 6 ( left side harness of PBU - blue with green )
I carefully opened the harness connector, removed the wire and grounded it to a good ground under the dash via jumper wire.
Bingo! A/C clutch finally came on! Nice and cold but I did not let it run for long as it seems to not cycle the compressor.
Question: Is there anything that can cause or fool the PBU not to signal / ground the circuit of the A/C clutch?
Or is this -- finally -- a clear cut case of a bad PBU , again. This one is only a month old rebuild from Programa ( I know - anything can fail! )
I just don't want to ship it back, they test and and say " no fault found! "

Evaporator temp sensor?

Sixto
98 E320s sedan and wagon
02 C320 wagon

I thought when that fails the compressor is stuck on?
But I've been wrong before.

The evap temp sensor is an NTC thermistor. If it is open-circuit, it will be infinite resistance and the PBU will think you're at -100000 degrees (maybe a bit exaggerated, but you get the jist).

The good news is that you've now proven the wiring all the way back to the PBU. "cycling" of the compressor is done based on the temperature of the evaporator. If the evap temperature sensor is screwed up or open-circuit, it can cause it, otherwise the PBU is probably toast.

So if the evap temperature sensor is screwed up or open-circuit it would make the BPU think its crazy hot and not shut off the compressor - correct?
In my case its not turning on the compressor.
Besides the sensor being open any other test or value I can check it for?
Plus - just took a quick look and can't find the part # to a new sensor.