I need instructions on how to bypass/disable the speed sensor on a/c comp on 1986 190d so that the Klima relay does not realize the compressor misses a beat now and then due to belt slippage or clutch slippage.

------------------
BRAD FRANCIS
1986 190D 160,000 mi.
SUMNER, TX

The only way to by-pass this function would be to either simulate it; which would be a trick or by-pass the whole relay. If thats your intention,depending on the year and relay jump the 15 or 30 to the 87 terminal.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Of course once you have done this, the compressor comes on whenever the key is on so it by-passes all the other problems that could be there. Not much good for diagnostics.

The problem with by-passing just the speed signal is that it is a dynamic pulsed signal and it is being compared in the electronics to the engine speed. It isn't a given at any particular time so it would be hard to reproduce and since the two signal aren't the same form (one is AC and one is DC they can't be just duplicated for comparison.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

[This message has been edited by Webmaster (edited 03-17-2000).]

THE COMPRESSOR RELAY CAN BE BYPASSED AS FOLLOWS,USING RELAY # 001 542 02 19 MAKE YOUR OWN JUMPER WIRES. TERMINAL #1 ON KLIMA TO #85 ON ICE CUBE,#10 KLIMA TO #86 ICECUBE ,TERM. #5 KLIMA TO #30 ICECUBE,AND #7 KLIMA TO #87 ICECUBE. CLUTCH WILL ENGAGE AND DISENGAGE AT PUSHBUTTON ASSY'S COMMAND.M.F.

------------------
M.F.

THANKS TO GERMAN AUTOMOTIVE M.F. WILL THE COMPRESSOR STILL BE CONTROLLED BY THERMOSTAT CONTROL WHEEL? ALSO WHAT ARE YOU REFERRING TO AS ICECUBE?

------------------
BRAD FRANCIS
1986 190D 160,000 mi.
SUMNER, TX

I have had to do this with 134 conversions because of the higher pressures. It does work. The ice cube is a generic term for the Bosch 5 pin relay. You can get one at any stereo shop... It will be controlled by the pushbutton and will cycle on and off yes./.

------------------
Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Speed Sensor on A/C Compressor
 

Problem. I've done this but dashboard control unit fails to output power to Klima socket pin 10. Tried a new control unit, no change. But does output power on pin 10 when Klima relay is installed normally. Something is missing that the Klima enables. Will investigate further.
John

The CCU doesn't output power to pin 10, it provides a ground.

I'm still working on this crappy mod. Bad enough it's compromised, it's not working as expected. I no longer think pin 10 is a ground, it's at 14 Megs to ground with a/c on. Pin 1 is ground, and I'm pretty sure Pin 10 should have power through the pressure switch in normal a/c operation. But instead, it's showing .75V. It could be that the system doesn't switch on until engine rpm is above 600, and the Klima is required for that. I have corrected my diagrams, and posted the latest but be aware that it's still work in progress:

http://www.peachparts.com/shopforum/diesel-discussion/386849-compressor-speed-sensor.html#post3735148

In the worst case, I can build a solid state circuit that can switch based on a .75V signal. It's getting to be a lot of work...

To bypass the speed sensor input I have used a klima from a w126/ 560/420, the multi belt system has no sensor circuit. Just plug and play, of course you lose belt protection

Diseasel300, Thanks for the feedback. Confirms what I was beginning to suspect from reading other posts elsewhere. GERMAN AUTOMOTIVE has the side of the cube relay coil opposite the side going to Klima pin 10 being connected to Klima pin 1, a ground connection. That led me to believe pin 10 would provide power.

So, instead of pin 1, I'll use the power source from pin 5 to connect to the relay coil opposite the connection to pin 10.

THE COMPRESSOR RELAY CAN BE BYPASSED AS FOLLOWS:
1. USING RELAY # 001 542 02 19 MAKE YOUR OWN JUMPER WIRES.
(P/No. Mercedes A 0015420219 / Hella 4RD004122-00)
2. TERMINAL #5 ON KLIMA TO #86 ON ICE CUBE, (Solenoid lead) (Klima power input)
3. #10 KLIMA TO #85 ICECUBE, (Solenoid lead) (Low pressure switch gnd input to Klima)
4. TERM. #5 KLIMA TO #30 ICECUBE,AND (SPDT common) (Klima power input)
5. #7 KLIMA TO #87 ICECUBE. (SPDT NO) (Klima output power to compressor)
CLUTCH WILL ENGAGE AND DISENGAGE AT PUSHBUTTON ASSY'S COMMAND

See note above, 10 is neither full power nor is it ground. Connecting to pin 5 means the compressor runs all the time, it's not a good choice.

I misspoke earlier when I said #10 was a ground. #10 is an output signal generated by the Klima and pulled down to ground by the ACC.

The Klima will output a voltage on #10 (~11V on my car) which the ACC pulls down to ground through the refrigerant pressure switch. It doesn't pull all the way to 0, I measure ~.8V like Frank does. The reason it doesn't go fully to 0 is because the switching is done by transistor in the ACC unit on '86+ models, they can't pull 100% to ground, the idea is to pull the signal "low" which tells the Klima to go ahead and engage the compressor.

So to recap, Klima generates voltage on #10 and if the pressure switch is closed (you have enough refrigerant), the ACC pulls #10 down to ground (low).

In my car, I found a failed darlington transistor pack in the ACC unit that caused it to fail to pull down. Rebuilt the ACC and it's been working like a dream.

That won't work with a Diesel engined car. The Klima also controls transmission kickdown on a Diesel.

I'm going to respond to this on the other thread, there are too many threads on this subject at the moment.

Speed Sensor on A/C Compressor
 

Guys: yes, the CCU puts a ground on pin 10 through the low pressure switch. With one side of the relay coil on Klima pin 5 for power and the other side on Klima pin 10, the relay will operate when the CCU is turned on and outputs the ground to pin 10. And if freon pressure is low, the low pressure switch will break this ground connection and shut off the compressor.
I've read some Mercedes material that says the compressor runs all the time when the CCU it is set for heat OR A/C and that the temperature of the air to the interior of the car is adjusted automatically by adjusting the amount of heat to mix with the air flow. This would explain my compressor being off when the "0" button is pressed but is on with every other setting. I didn't observe the behavior of the compressor with the original Klima installed to confirm this to be correct. I will. Anyone else observe this?
I am now researching the diesel kickdown behavior that turns the compressor off under hard acceleration that MXFrank mentions.

The compressor should be off when in Economy (EC) mode. Every other function it should be running unless the coil gets cold enough to operate the evaporator temp sensor at which point the compressor starts cycling. The air should never be colder than ~42˚ if the system is working properly.

The microswitch on the accelerator linkage will also drop the compressor out at WOT

The overheat sensor in the head will drop the compressor out when it operates. The trigger point varies on year and model.

The Klima also checks the speed sensor on the compressor and will drop the clutch out if it senses that the compressor has stalled.

The Klima as designed also adds a delay when the engine is started so that the compressor does not engage until 600 RPM is reached.

So the Klima actually does do some important things, but most of the functions can be replaced with simple relays.

Thanks, man! Also, I'd like to direct this discussion back over to the one you and Mxfrank were having about this topic. I've attached my version of your diagram of the dual relay set up to add some protective diodes. Let's go back there, okay?

Go here: http://www.peachparts.com/shopforum/diesel-discussion/386849-compressor-speed-sensor-2.html#post3735539