Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hi Peter, my name is***** 7 powers the mono valve and the climate control. If you do not have 12V to the mono valve or the climate control with the key on you must have a problem with the fuse circuit. Have you cleaned or replaced fuse 7 yet? A bad fuse connection could cause this problem. If the fuse connections are good you will need to test for power to fuse 7 when nothing is working. If you have no power to the fuse you may have a bad ignition switch.
Let me know what you find.
If you have actually tested the wires to the mono valve and neither wire has 12V then the problem has to be the fuse circuit which comes from the ignition switch then to the fuse and then to the valve and the climate control unit.
Okay, so now you need to go to the fuse and do the same test. If there is no power to the fuse then I suspect the ignition switch is faulty. When testing for power make sure you are not testing across the wires. Connect your voltmeter or test light to ground and probe the terminals with the other lead.
Hi Peter, the valve and the control get power directly from the fuse. It sounds like you have no power leaving the fuse box. If you have replaced the fuse and cleaned the contacts I would suspect a bad fuse box. I'd lift up the box and test for power on the wires leaving fuse 7. It's a straight shot from the fuse to the valve and control unit. This has to be a bad connection at the bottom of the fuse box.
It doesn't make a lot of sense but if you are sure of your tests there has to be a fault with the circuit leaving the fuse box. I've attached the wiring diagram below. Notice how the wire from fuse 7 goes directly to the components. If you have 12V at the fuse you must not be getting 12V from the fuse box.
How are you testing for power at the mono valve?
Are you connecting the meter across the two terminals or are you connecting one lead to ground?
You can't test it that way. You need to test for 12V to the individual terminals. Connect the meter to ground and probe each terminal for 12V.
If you are testing across the two terminals you are testing for both power and ground. If you test the individual terminals and one has 12V then we are lacking the ground from the climate control unit. If you have 12V on one wire then our fuse circuit is fine. If that is the case we are lacking a ground from the climate control unit.
Hi Peter, glad you got it squared away. I mentioned that the climate control unit was the likely problem if you had 12V at the mono valve. I was going on your statement that you did not have 12V at the mono valve. I asked you twice during our exchange how you were testing for 12V. The problem was that you were testing across the terminals instead of testing the individual leads.