Auxiliary fans short AC compresor? - PeachParts Mercedes-Benz Forum

Racekar · #1 09-14-2007, 06:48 PM

I was noticing that my fans dont come on, I checked the blue/grey temp sensor and it's ok. When I reconnected the plug to it the fans came on high, right away, even though it was only 85 degrees. I played with the wire and when bent it turns on and off so I assume it's a short in the wire that goes to the sensor. It seems to go under the intake manifold, hard to change?

Also the worst thing is that when the fans come on, the AC compressor shuts down. Is this suposed to happen? I have a choice of having the fans on all the time and NO AC, or no fans and AC. My AC was working fine before this, I just wanted the car to run a little cooler in the summer with the AC on. Is this a simptom of the 1995 W124 wire iinsulition issue?

Arthur Dalton · #2 09-14-2007, 06:54 PM

Sure is..search "Wire Harness"

Racekar · #3 09-15-2007, 10:55 AM

Why would the AC compressor clutch stop when the fans come on? When people wire up the fans with a switch the AC doesen't stop when the fans come on? Does anyone know what harness I need and how complicated it is to replace. If this is the only problem could I just trace out the wires and fix this?

Arthur Dalton · #4 09-15-2007, 02:34 PM

Quote:

Originally Posted by Racekar

Why would the AC compressor clutch stop when the fans come on? When people wire up the fans with a switch the AC doesen't stop when the fans come on? Does anyone know what harness I need and how complicated it is to replace. If this is the only problem could I just trace out the wires and fix this?

There is the possibility that the reason for comp cut out is too much high side pressure..The fan comes on to allieviate the condenser pressure, but that pressure may be beyound that, causing the high pressure comp safety sw to cut out.
The question is "Does the comp cut-out as soon as fan is activated?
If so, disconnect the fan pressure sensor leads and re-try..That will tell if you have an electrical feedback problem vs too high a high side pressure ..

Racekar · #5 09-15-2007, 06:16 PM

No the pressure is ok, I checked it and I disconected the sensor and it still stays off when the fans are on. I think the wires are shorting. anyone just replace some wires, I realy dont want too change the whole harness

Arthur Dalton · #6 09-15-2007, 06:22 PM

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How can the fans be on if you disconnected the sensor ??

Is that what you are saying?

juribe2 · #7 09-15-2007, 11:09 AM

I know you have a different engine but since your car is 1995, I suggest to read this:

http://www.peachparts.com/Wikka/M104WireHarness
http://www.peachparts.com/shopforum/showthread.php?t=128181

Racekar · #8 09-15-2007, 01:35 PM

I read these threads, it would seem that the gasser is much easier to fix since most of my wires are under the large intake manifold that the 606 diesel has. Has anyone done this themselves, do you need to remove the intake?

wscheffer · #9 09-16-2007, 02:44 AM

If the w124 setup is simmilar to the w126 then the fans could have a jumper wire on at the thermostat housing from a PO causing the fans to be on when the ignation is turned on. Cheap fix for failing switch!

Racekar · #10 09-16-2007, 10:14 AM

If the wires were shorting in the wire harness the closed circuit would then turn the fans on high, which I think is my problem. Still does not explain why the AC comprossor shuts down when the fans come on.

Is that a large harness and again do I need to remove the intake manifold on a 606 to fix it?

If I do, what else should I change? fuel lines? glow plugs? ect?

I would like to only do this once but do it right.

Arthur Dalton · #11 09-16-2007, 10:26 AM

>
Of course it does explain it. The high fan is triggered by the ECT sensor..this is a thermistor sensor and it is the temp input to the ACC controller..that is why I asked you about the Low fan sensor at the drier .That is also aux fan , but LOW/AC fan circuit.
To track down which circuit [ low/high, there are TWO fan circuitas on that chassis]] , you simply disconnect the sensor I mentioned ..then you know which fan circuit is cutting out the comp.

You could have a shorted ECT sensor and the CC panel would cut compressor. But if you want to change the whole harness before doing a couple of these simple test, have at it.

Racekar · #12 09-16-2007, 10:35 AM

I disconected the pressure sensor by the condensor, the one with the 2 black spade connectors going to it. The AC stayed off. There is another sensor below it (Blue) with a red cover and 2 wires going to it. I could not get the cap off so I did not want to break anything else and left it alone. Where is the other sensor located.

I am a litttle disturbed by the fact that there are no good manuals for this car. I have rebuilt motors, including rotarys, from a good workshop manual and a hayes manual. With out the help of this and othher forums it would be very difficult for a person to figure out whats going on.

Arthur Dalton · #13 09-16-2007, 10:51 AM

Quote:

Originally Posted by Racekar

I disconected the pressure sensor by the condensor, the one with the 2 black spade connectors going to it. The AC stayed off. There is another sensor below it (Blue) with a red cover and 2 wires going to it. I could not get the cap off so I did not want to break anything else and left it alone. >>

Wrong sensor ..the sensor you disconnected is the comp cut-out, so of course the comp stops.
The sensor I want you to disconnect in my Diagnosis step #1 is the one you think you have to take the cap off...there is no cap, that sensor is a sealed unit with a pigtail wire harness coming out of it..that is where it gets disconnected ..at the end of the pigtail [ 2 white connectors sleeves]
That is the LOW FAN CIRCUIT ..once we know if that test effects the complaint, we can go on to Diagnostic step # 2 ..which will be the ECT sensor at the termostart housing..that is temp Input to ACC conrol panel and also conterls HIGH FAN CIRCUIT>

I am a litttle disturbed by the fact that there are no good manuals for this car. I have rebuilt motors, including rotarys, from a good workshop manual and a hayes manual. With out the help of this and othher forums it would be very difficult for a person to figure out whats going on.

I agree..but when you ask a question and someone who is versed on this system and has a schematic pulled up on your chassis and is trying to tell you how to diagnose it, it would be better for you to listen..twice you have refutted my attemps to give you the diagsosic sequence steps to narrow the problem.
If you just did the test and report the results of each test, I would tell you what the possibles are...

JimF · #14 09-17-2007, 11:07 AM

Quote:

Originally Posted by Racekar

I was noticing that my fans dont come on, I checked the blue/grey temp sensor and it's ok. When I reconnected the plug to it the fans came on high, right away, even though it was only 85 degrees. I played with the wire and when bent it turns on and off so I assume it's a short in the wire that goes to the sensor. It seems to go under the intake manifold, hard to change?

I see you posted here on your 'wiring' problem.

The fact that you can "PLAY" with the wires and get different results shows that you need to change the wiring harness asap! It CAN and WILL do some damage to ECUs so you are playing with a loaded gun!

It's NOT difficult job to replace the harness as many here have done it. The links in post#4 show the harness in detail.

Tnx to Arthur for your help to get him squared away.