pic, What relay is this next to the Klima relay that controls the compressor. My compressor wouldn't switched to 134r freon,new dryer and evaporater and compressor. Jumped compressor from +on battery and it worked. Jumped the low pressure lines together and no engagement. I pulled a 10a fuse from this relay, and put a 15a cause that was all i had, and the compressor came on and worked for a day. What function does this relay have . also in what relation to the compressor or Klima. Today I changed it to a 7.5 fuse just in case the 15 is why it stoped again,maybe shorting the Klima. Any thoughts on the circled relay in the attachement. 1985 300sd 126

There is no picture in the thread. I am assuming you are talking about a silver relay with a 10A fuse in the top of it????
If this is what youmean that is the OVP relay. Overvoltage protection relay. It protects many things in the car from too much voltage, like your ABS brake computer.
Only a 10A blade type fuse should be used in it. Is your ABS light on?

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John
1986 300sdl
1985 380se

I dont know what happened to the pic but here it is now. Sorry all. Ray M

Attached Thumbnails

 

Does it control anything else besides the compressor and the ABS brake computer. I hope I don't have to chase anything else down in the car. Is it possible I blew that fuse or the klima when jumping the compressor to the + terminal on the battery to see if the compressor was working.

I will check my wiring diagram tonight when I get home and see what else it protects unless someone else chimes in before then. I know that on my 85 380se gasser, it protects the ABS computer, the idle speed computer and the fuel injection computer.

__________________
John
1986 300sdl
1985 380se

And the Climate Control Unit (Push-button) [A/C's Brains].

When you said you, "Jumped the Compressor",from the," + (I assume Positive)
on the Battery", ...Specifically (VERY important) Where did you apply the
12 volts Positive [To which WIRE or TERMINAL] ? If you put the 12V to
anything OTHER than the positive pole on the compressor (OR IT's WIRE)
you may have trouble.

That positive pole on the Battery is not what it seems...look at it as a direct
connection to LIGHTNING.Everything in the engine compartment is negative
ground and all it take to un-leash havoc is the threat of a POSITIVE connection.

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'84 300SD sold
124.128

after an exhaustive night reading then trying what I read, I seperated the klima and found where it needed resaudering. Like is great now. Thanks to all who've helped on this thread and those i researched. I'd hav ended up bringing it to my mechanic buying a new klima and paying for 3 to 5 hrs of labor probably. Thanks RAY M
Ps I now have 2 black box relays that i think controls the tac and a 380 1985 instrament cluster that has 125,000 and some relays I bought and can sell if needed. pm me if you need one.

I just looked through the wiring diagrams for your 85 300sd and this is what the OVP relay controls:
1. ABS light
2. Charging light
3. ABS Computer
4.ABS Hydraulic unit
5. EGR control unit
6. Cruise Control

Of specific concern is that if the EGR control unit is not getting power from the OVP relay, you then cut the power to the A/C Compressor. You see, the EGR control unit and the kickdown switch shut off the A/C compressor when you floor it. I am guessing if the OVP is not supplying power to the EGR computer, you then have a situation where the compressor is off.

I would replace the OVP relay with a known good unit and see if all starts running well again.

__________________
John
1986 300sdl
1985 380se