Requesting help Identifying a diode and knowing its condition.

Thread Starter


Joined Feb 6, 2024
Hello There!

I tried to jump-test the clutch in the AC of my car, connecting the plug directly to the battery, not knowing the pole, I went for my best guess (brown ground, green live) and just did it for a split second. Not only It didnt work but also something in the plug smoked and I quickly took it off.

My concern is if that was enough to burn it. It didn´t inflate or melt. But I can´t test if current goes the proper way, because the whole assembly is sealed and with a tester I have same resistance both ways (due to the coil). In case it´d be wise to replace or remove it, how i can identify it? It only reads 0 0 so either the other numbers are erased or I don´t know what to think. It´s a for a 12v DC circuit, so I bet there are a range of safe replacements to use.

tltr: can someone guess the values of that diode and know from the looks if that one is burnt?

Attaching the best pictures I could take of it:


Joined Sep 22, 2009
As you have guessed, it is difficult to guess the identity of the diode. I dont know what that connector is or what the diode is doing in there but if desperate situations require desperate measures.

So, did I understand correctly that there is a coil in there in parallel with the diode?

You check the diode with a diode test setting on a multimeter if you disconnect one end of the diode. This will give you an idea of if it is burnt out and needs replacement.

Looking at the diode, sizewise, it looks the same size as a 1N4007, you could try to replace the diode with a new 1N4007. I am just not sure if anything else has been damaged downstream besides the diode/inductor.

Thread Starter


Joined Feb 6, 2024
Hello! thanks for your reply!

Problem is i could only test the diode by cutting one end to isolate it from the coil (yeah they are in parallel). However, i managed to figure the polarity by checking ground continuity in the female plug that connects to it (too bad i didn´t try it before).

So far, the coil seems to be working fine now, so I will leave it as it and if something goes wrong will find a 1N4007 and replace the old one.

Another test I can think of ATM would be checking current consumption when jumped (now with proper polarity). I know the current draw is around 3 amp. So if it´s spot on, i could sleep at ease hehe.

Again, thanks for the help, keeping note of your suggestion, in case something goes wrong.


Joined Dec 13, 2021
The diode across a coil is probably a back emfs suppressor, may be,
By connecting volts backward, you forward biased the diode,
With out the diode , the circuit will still work BUT, each time the circuit is switched off, a large back emf is going to be applied to what ever is driving this signal, probably fairly soon blowing that ,
If its a engine management or such like , that will be real expensive. Time for a new unit I think,

Thread Starter


Joined Feb 6, 2024
The good news is that the device is working, so I assume the diode didn´t blow (or if it did, it just stopped working, instead of shortcircuiting).

As for the EMF suppresion, you´re probably right, but this isn´t an engine, it´s just an electromagnet that when excited pulls a plate against a clutch inside a pulley, to engage a belt driven air conditioner compressor in a car.

If ever something goes wrong with it, first thing I´ll do is removing the diode, and if that causes problems, replace it with another.