Manual ball valve for hot water - heater core hose - Page 2 - PeachParts Mercedes-Benz Forum

Diseasel300 · #16 10-27-2018, 10:56 AM

As mentioned above, digital meters can, and often do give false results. They don't load the circuit at all and pick up any sort of stray voltage or static and report it as a real value.

A test light is a good idea, an old school analog meter is another one (if you know how to read it).

The coil is either good or bad. Test the coil for resistance. I'd expect it to be somewhere around 10Ω or so as a guess. If the coil is good, it isn't your problem.

Testing the voltage at the coil is done differently than you were doing as an operational test. What you proved is that the ACC is switching, or the coil is open (resistance measurement will confirm or disprove that).

With the coil connected, fiddle with the ACC to energize or de-energize the monovalve and read voltage across the 2 coil terminals. If you read 12V or close to it, the ACC is energizing it. If it isn't, you'll read ~0V.

Think of electricity as water flowing through a garden hose, it's all about potential. If you have the end of the hose open, water can flow through. Pressure is higher at the inlet side than the outlet side due to the restriction of the hose itself. If you close the end of the hose, the pressure is the same at the inlet as it is the outlet. There is no pressure difference in the hose and no water flows.

The pressure difference is your potential voltage (the voltage difference between the inlet and outlet of the circuit). The flow rate is your current (the amount of power flowing through the circuit). If the ACC is switching, you have a ground (or close to it) at one end of the monovalve coil. You should therefore read a potential voltage across the coil (nearly battery voltage). When the ACC is not switching there is no ground reference to the coil, therefore the 2 terminals on the coil have the same voltage and there is no potential difference (0 volts).

What trips a lot of people up troubleshooting these systems is that the switching is done by transistors on the ground side of the circuit. A transistor works on current. If the circuit is not complete and current cannot flow through it, you can get some really strange results, especially if you're using a digital meter to do the testing.