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Car Forum / Mercedes-Benz Cars / July 2006tach problem PLEASE Help
I have a problem with my rev counter,on my w201 190 2.5 diesel. I took out the cluster already to see if there's something wrong with the rev counter but I didn't notice anything,I bought a used one from internet to see if there is a fault in the tacho it self but it still don't work. I changed the rev per minute sensor located at the bellhousing and still no signal. I took the car to my electrician and told me the rpm sensor is ok,(is sending impulse).The problem is that the impulse is not reaching the tach.there is no impulse to the tacho.We checked all the fuses and they are all fine. Is there a relay related with the tach? Some thing that my electrician is suspecting is that the klima relay is not letting the impulse going to the tach, Is that True?Does the Klima relay playing part with the tach? Thanks Did you change the fuse? Just looking at it means nothing. The fuse is alright,I changed it already > The fuse is alright,I changed it already Not familiar with that mode, but on the earlier 116 diesel MB had an electronic widget that converts the pulses to the proper signal for the tach. It is located on what appears to be a test cap inside the engine compartment, the driver side fender area. I guess the test connection is so MB could hook up maybe a tach, timing light, etc. The top of the cap has the widget and screws off. Mine went bad and the tach started acting eratic, then finally died. Got a new one at MB. I don't recall the wiring diagram and am not sure if Klima relay is up or down stream of the tach, but it is a possiblity. Klima relay controls A/C compressor. The A/C design incorporates a logic to stop compressor if it is found to be "frozen". What does it mean? There is a rpm sensor at the end of the compressor. Klima relay constantly compares the rpm of engine and compressor (after a half second delay after both start turning). If it is found to be more than 20-30% (don't recall the exact value mentioned by manual) different than spec, the relay cuts off the compressor clutch and the A/C can never get truned on until engine is restarted. This is to protect the single belt. AFAIK, all MBs in the 80s with single belt have the same logic. Later models are probably the same. Sometimes this design causes no A/C when the pulley slips due to oil/dirt, or when the tension/belt is loose. If A/C works only for a brief period affer start and it can not turn on again until restart, it is typically this reason. Does the A/C work? > I have a problem with my rev counter,on my w201 190 2.5 diesel. > [quoted text clipped - 13 lines] > Is that True?Does the Klima relay playing part with the tach? > Thanks Hello, Thanks for your information, Yes most of the cases the A/C shut off and don't switch on again until I restart the car,Now it's not working but I think it less on freon,I will go for a repair. This turn off can also be triggered by two other sensors... one is pressure switch which if you don't have enough pressure, compressor will stay off. The other sensor on modern car will sense ice at the evaporator and will shut off the compressor too. The one Tan mention is to protect the engine belt in the event the compressor clutch is siezing. If the 190D has a tach amplifier that is most certainly the problem. It can (sort of) be "repaied" with a hack: http://articles.mbz.org/electric/300tachamp/ But that may only last a year of three. A new tach amp fixes it for a couple of decades... agai IF this car has one. I'm guessing...  SignatureNeed Mercedes parts? http://parts.mbz.org Richard Sexton | Mercedes stuff: http://mbz.org 1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net 633CSi 250SE/C 300SD | http://aquaria.net http://killi.net Hi thanks, The 190 does not have a tach amp. |
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