What I mean by turning the compressor is turning the clutch part of it.

Vin is WDBDA28D3MF742699

Andrew

 

Turning the clutch doesn't help you decide whether the pump is seized unless 12v is applied to the clutch.

 

I went through the first part of the info snanceki gave me (test on the AC relay plug).

Voltimeter on terminal 5 and 1 gave battery voltage: power for the relay.

Shorted 5 and 7: clutch engaged. I started the engine and compresssor was working fine, I could see some R134 flowing through the dryer (guess I didn't get it all out).

With engine running (forced low idle), voltimeter on terminal 9 and 11 gave AC voltage (>0.3V, 700-900 RPM) with clutch engaged: Compressor's speed sensor works.

With engine running (high idle), voltimeter on terminal 1 and 2 gave DV voltage (about 8.7V) and AC voltage (about 5.4V): speed signal TD is good.

And finally: Voltimeter on terminal 5 and 10 gave nothing: pressure switch. Could this be because the AC system is not full? I also couldn't find continuity between terminal 10 and the pressure switch.

Edit: terminal 5 is ground.

Andrew

 

Andrew.
You appear to have missed out the check on the pressure switch terminals at the start of the diagnostics tree. So what have you learned?

Clutch works when control unit is bypassed. So why doesn't the control unit work under normal conditions?

Appears to be due to no signal on pin 10. I believe this signal (ground) comes from the pressure switch.
What happens if you ground pin10 (CAREFULLY). If the compressor clutch engages it looks as though the pressure switch S31/1 circuit is not working.

The test you ommitted ensures that the pressure switch has a good ground on it. This will assist in determining if it is the ground, the switch or the wiring between the switch and cutout is at fault. You state no contionuity between Pin10 on N6 and the pressure switch. You need to find out why!

Did you notice that the voltage from the speed sensing system (Pins 1 and 2) is different if an ISC is fitted! 2.8 vs 4v AC. I wonder why? You were measuring 5.4v!! You also ommitted the speed sensor resistance check. 550 to 650 ohm. so I don't agree that the speed sensor is working correctly.

What about the temp sensor check?

What did your visiting MB techs say about your problem. BTW How did you force the reduced idle you referred to?

Stuart

 

Voltage on the pressure switch pins is about 7.5V and the other is 0V (millivolts). Supposed to be 12V right? The zero volts could be the high pressure side being under 3 bar, by why would the low pressure side be only 7.5V? What kind of pressure gauge do you use to test the AC pressure?

Not sure what you are wanting me to do to pin 10... Are you wanting me to ground pin 10 while the relay is in?

I was thinking the speed sensing system would most likely be higher because I let it run at the high idle (3200). But I redid the test with forced low idle and I saw no change in voltage. It's resistance is 651 ohm... Where is this sensor located? In the event that the speed sensor is bad, could this effect idle or is the TD only used for the AC?

I don't have a terminal 12 to test the temp sensor... So I figured it couldn't effect the AC.

Techs recommended changing the ICV and said the AC is more than likely unrelated.

Forced the low idle by blocking the ICV.

Andrew

 

snanceki and I have made some progress. We have got the AC to come back which turned out to be a faulty pressure switch. However, we have ot been able to fix the idle. I have been doing research on the idle though. I have found out which components are suspect for high idle in MBs. They include:

Idle control system components
Coolant temperature sensor
Throttle position sensor
TDC sensor
EHA
Differential Pressure regulator
Intake air temperature sensor
Atmospheric pressure sensor

The idle control system components and the coolant temperature sensor have tested out good. I need to know how to test the others. I also need to know where the differential pressure regulator and the intake air temperature sensor are located. I bet the problem lies with one of the sensors as the voltage going to the ICV is way too high.

The only other thing I can think of is possibility a short in the wire going to the ICV so that it is recieving voltage from another source other than the ECU. Let me get something straight, the black box in front of the ECU is the the ABS computer, right? It seems like when I started working with this problem I found continunity between one of the pins on ABS computer plug and I believe terminal 2 on the ICV plug, is that right? I didn't realize this was the ABS computer so I didn't think anything of it... I'll check this again tomorrow morning to be sure.

Andrew

 

Since you are all probably interested in what the problem is on my 190e i figured i would go ahead a share. I gave up and let the dealer have at it for 3 days and requested that the head tech take a look (because it is not the first time i have brought it there). Problem is coming from the fuel distributor which is leaking a good amount of fuel into the mas sensor and into the intake manifold. I ordered the part (now i'm broke) and i will let you guys know how it goes when i get it. More than likely the o2 sensor is reading rich causing the ecu to open up the icv, that's why the idle drops when i plug it (not enough air for the amount of fuel).

Andrew

 

Hi,
If fuel is leaking into the inlet system (i.e. MAF) it is not surprising that you have a high idle. You've got your own auxillary carburettor!

You never mentioned the possibility of a leak.

Anyway, I'm sure problem will be fixed even if you are broke.

You are now an expert on this specific problem...

Stuart.

 

I love having both fuel injectors and a carburettor!

Leak? I never actually considered it. I was too centered on the ICV. I also had an air leak as well is the rubber boot just under the MAF which after replacement actually raised the idle to 4000 [&:]. Not sure what happened there. The dealer also made some adjustments to the intake system which lowered the idle to 2000 with my cheap fix off. They did a test on the fuel and electrical system. Other than the fuel distributor the fuel system is in good shape and the electrical system has both a bad OVP and the wrong ECU (has the one for the 86-87), how bad is that? Also found a bunch of mismatched connections, which they fixed. Also, I am not sure how this is even possible, but the transmission in this car is not the correct one. It seems like my old '85 nissan 300zx turbo had two different standard transmissions between years that are not inter-changable, i figured MB would be the same. Is that bad, the car runs?

Expert? Nah...

Andrew

 

Well, the new fuel distrubutor is in with no change in idle... I put the correct ECU in, but that didn't help either. I am going to buy a new OVP, but I am doubtful that is the problem. After doing some more research, I discovered that a common problem with the 16V versions is a bad air flow potentiometer which causes an idle above 3000. I am going to look for a new MAF, hoping that the 8V can have the same problem. I'll let you know.
Andrew