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Car Forum / Mercedes-Benz Cars / July 2005Blower Motor AC Diode Sensor Switch
Can anyone tell me what the AC diode sensor switch (the little wafer with 2 connectors) that screws on to the end of the blower motor in my 107 does? I couldn't get the blower to change speed, and one of the connectors on this diode broke when I removed the wire to check it. I soldered it back together, but now I can't get any continuity reading across it. Thanks for any help. Series resistor? >Series resistor? No. The part is called an A/C (Air Conditioning) Diode Sensor Switch. ar #002 821 1851. >>Series resistor? > >No. The part is called an A/C (Air Conditioning) Diode Sensor Switch. >ar #002 821 1851. Usually diodes in series with devices are used to protected the device from power supply of opposite polarity But if one inverts the battery polarity it's going to damage a lot of other things. It can also be used to sense the current to the A/C by measuring the voltage across the diode. Vlad Vlad, Thanks for the info on this diode. Does the fact that I can't get a current reading across it indicate that it's bad: I'd hate to replace it if I didn't have to. >>>Series resistor? >> [quoted text clipped - 8 lines] > >Vlad Measure the resistance of the diode disconnected from the circuit. It should be less then 20 Ohms one way, then invert the leads an it should be more than 100 Ohms. In other words it must be almost a short circuit one way and almost an insulator the other way. You say that you have no current across .Are you talking about current or voltage? I get the impression that you mean voltage when you refer to current. If you have about +12 volts on one side and no voltage on the other side, the diode is defective or connected the wrong way. In order to have current you must have a load. Vlad >Vlad, > [quoted text clipped - 14 lines] >> >>Vlad >Measure the resistance of the diode disconnected from the circuit. It >should be less then 20 Ohms one way, then invert the leads an it [quoted text clipped - 9 lines] > >Vlad Vlad, I placed each lead from a multi-tester on one of the diode's fins and set the mutli-tester to test resistance: i.e., when I touched the leads together current flowed from one lead to the other through a circuit that showed essentially no resistance. However, when I placed one lead on each fin of the diode, the meter did't budge, regardless of which lead i placed on which fin; i.e., no current flowed evidently because there was essentially infinite resistance or an open cirucit. Am i doing something wrong, is the diode bad, or cannot I not check it like this? Thanks again >>Vlad, >> [quoted text clipped - 14 lines] >>> >>>Vlad >>Measure the resistance of the diode disconnected from the circuit. It >>should be less then 20 Ohms one way, then invert the leads an it [quoted text clipped - 19 lines] >of which lead i placed on which fin; i.e., no current flowed evidently >because there was essentially infinite resistance or an open cirucit. Then , the diode is defective. Someone has suggested that you can short the wires( the diode) and everything will be OK. He is probably right but without knowing the reason for the existence of the diode I can' t recommend it To be safe, do not run the car's engine with a shorted diode. If the diode is defective, why ? Did you make a short ? Old age ? Not likelly. If the motor is defective you will burn the new diode. You should be able to run the electric motor before installing the new diode by connecting it directly to the battery. If it runs without getting very hot ,then it's safe to install the new diode. You could measure the current before installing the new diode but if there is a short you probably burn the meter. What I some times do is to temporarily install a 12Volts lamp (high beam) in series with the circuit ( in your case replacing the diode). If the light becomes very bright, measure the voltage at the lamp's terminals. If it is 12 volts at one side and zero at the other side, you have a shorted motor. If you have 12 Volts on one side and a few volts at the other side and the motor slowly runs, it should be safe to install the new diode. If you want to go this way, install the lamp and report the type of lamp you are using and the voltage at the terminals. Vlad >Am i doing something wrong, is the diode bad, or cannot I not check it >like this? [quoted text clipped - 19 lines] >>>> >>>>Vlad you can just jump the wires together and not have a problem > you can just jump the wires together and not have a problem Either that, or you will discover why they use a diode instead of a wire. >> you can just jump the wires together and not have a problem > >Either that, or you will discover why they use a diode instead of a wire. Yes. The diode is there for a purpose . Vlad
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