Tuesday, May 08, 2018

Automotive Relays Explained

Testing Automotive Relays Explained

Testing automotive relays before replacing them is a good idea and it’s not to difficult.
In most cases if you miss diagnose the electrical problem and buy a new relay and it doesn’t fix the car, you’re stuck with the part you didn’t need.

This is because most auto parts stores have a policy that electrical parts are non-refundable. The good news is, there are several ways to test automotive relays.
Now you’ll be able to verify it’s bad before you replace it. The picture on the right shows a bad four terminal relay I discovered during a no start diagnoses. This starter relay actually had a material failure in the copper contact blade that completes the circuit.
It cracked causing an open condition resulting in no current flow to the starter motor solenoid.
I don’t see this type of relay failure often. Sidebar: They made this relay in China. For a long time most were made in Germany by the Bosch company.

We might see more failures like this in the future as car-makers cut costs in an attempt to stay competitive with the Korean car builders like Hyundai and Kia. To me this is an unusual failure, With most relays, when we remove the cover, you’ll find burned contacts or melted winding.
The contacts can also become corroded and turn green in color. If it’s severe enough the device won’t flow current or complete the circuit as intended. This condition can stop the car AC compressor clutch from engaging.
So the first way of testing automotive relays is by actually removing the cover and performing a visual inspection.
Note that some companies actually glue the cover on to prevent tampering and seal out moisture. In some instances you can put on a pair of mechanics safety gloves, then take a utility knife and carefully cut the adhesive seal to see inside.
I should also mention some manufacturers make it really hard to get the cover off and in rare cases it’s near impossible. Luckily there are two more good ways of testing automotive relays.

Swapping Out the Old Relay

In some scenarios you’ll need an automotive wiring diagram or at least a professional grade car repair manual that will indicate exactly where the relay is located.

When you find the one you suspect as defective you might see other ones just like it in the relay center. Take a close look at the part number, example 17008-4915. You can locate another one with the same exact part number and swap locations.

This way you can retest your malfunctioning circuit and verify it’s now working with the swapped part in place. You can also check the circuit you swapped from is now not working.
If this is the result, then congratulations, you have definitely nailed down a bad automotive relay.
Car makers are always trying to hold down the cost of manufacturing.

They often use the same part number components for many different circuits in the vehicle. This allows them to mass produce these electrical parts and just plug them in during assembly.
Use this to your advantage and swap them out.

The way that an automotive relay should be tested is to actually break out an automotive test meter and confirm proper operation of the relay.
When testing relays it’s important to remember they’re not as complicated as they seem and neither is the test procedure. In fact, they even make a plug in tester that shows a red light if the relay is bad and green if it’s good. This tool is on the right.

How Relays Work in Cars

Most relays have four or five terminals. The job of this electrical component is to physically connect two of those terminals on command to allow electricity to flow to the load in the circuit.
The load would be something like an ac compressor, starter motor, fuel pump and so on. Again you’ll probably need an automotive wiring diagram to determine which terminals connect to which wires.
Basically, we use two terminals to energize the magnetic coil that pulls a contact closed. This allows the electrical current to flow. When properly testing automotive relays you need a 12 V battery to energize the coil.

Take 12V and apply it to one side of the coil and a good ground to the other side. I have a car battery for bench testing but you can disconnect the one in the car and use it for this test.

With the coil energized the switch should open or close and you can verify the current flow by using a meter set on the continuity check setting.
In this mode your meter automatically beeps when the circuit closes and working properly.
If this test fails and the switch doesn’t open and close by energizing the magnetic coil, perform another test with an automotive meter. Physically check the resistance of the magnetic coil by selecting the resistance mode or Ohms on your meter.

You touch one lead to one terminal of the coil and the other lead as well. A magnetic coil in an automotive relay should have just about no resistance. Your meter should read close to zero ohms. Testing automotive relays takes a little practice but is well worth the effort.

These types of repairs can be very expensive at your auto repair center because they require a good amount of skill level. This is also an automotive repair that is clean and exercises the brain.
If the air conditioning relay fails the car AC system blows warm air.

This next link will take you to some additional information on the youfixcars.com site so you can learn about automotive electrical systems.

If you would like to see what else is covered on the website you can visit this next link that will take you to the Homepage for YouFixCars.com.

# posted by Kerminator @ Tuesday, May 08, 2018 0 comments

Electronics - 1 - Finding grounds

September 21, 2010 Mark Gittleman

How Ohms law Works

This week I wanted to talk about ohms law since I mentioned it in last week’s post about taking the ASE automotive electrical test. Although you may not use this formula while you are solving automotive electrical problems if you plan on passing the electrical test, understanding the law and its principles can really come in handy.

Electrical Circuit

George Ohm is accredited with the term. He was a German mathematics professor and in 1827 wrote a book that included the explanation of how electricity behaved. His thoughts have become the basis for a true understanding of how electricity works.In his book he states that it takes 1 V of electrical pressure to push one amp of electrical current through a 1 ohm resistor. This equation is the basic law of electricity and is known as ohms law. In a practical example a simple electrical circuit can be connected to a voltage source by conductors better known as wiring.

The resistor could be a lamp and the voltage source could be the battery. The two are connected by wiring. In any electrical circuit resistance (R) current (I) and voltage (E) are related to each other in how the circuit will perform. This can be converted into a mathematical equation. This equation can be applied to the entire circuit or just a section of it.

How ohms law works

Ohms Law

The equation is (E) over (I) times (R). When any two factors of the equation are known the third factor can be determined by using ohms law and the mathematical equation. If you are trying to calculate voltage this would equal the current measured in amps multiplied by the resistance measured in ohms.If you are looking for the amperage you would then take the voltage and divide by the resistance that is measured in ohms. To find the resistance you can take the voltage and divide by the current that is measured in amps.
As an automotive mechanic it is important to understand ohms law because it truly explains how an increase or decrease in voltage, resistance, or current can affect the operation and performance of an automotive circuit.

Practical application of ohms law

Finding Voltage

Using the lamp example from above let’s pretend that it is a parking light. If you are trying to calculate how many amps the bulb uses you can measure the resistance of the parking lamp using an automotive meter. You can then take the battery voltage of 12 V and divide it by the resistance to find out exactly how much amp’s the bulb uses.You may be wondering how this can apply to the real world.

What would happen if the resistance in the circuit increased due to a corroded or damaged connection to our parking lamp?
If the corroded connection added to ohms of resistance to the parking lamp circuit the amount of amps flowing through the bulb would be decreased.

If you were looking at this bulb it may not seem to be shining as bright as the other bulbs on the vehicle. With this knowledge you now start checking electrical connections in the parking light circuit that has the dim bulb. And you know what you are looking for an increase in resistance causing a decrease in amperage.

I don’t claim in any way to be an automotive electrical instructor. In fact I am just a mechanic that will be taking the ASE recertification for auto electrical systems for the fifth time. On my other website I have about 10 pages that dive into more automotive electrical theories that you may find helpful for solving car electrical problems. If you are looking for more of the most recent articles on this blog this next link will take you to the homepage from this article about ohms law.

====

What is a Grounded Circuit

A grounded circuit is similar to a short circuit. In that the current bypasses part of the normal circuit path. But in this instance, by going directly to a ground source. An exposed wire directly touching ground may cause this.Also part of the internal circuitry within an electrical component can come in contact with a ground source by touching the housing of the unit itself. You have to remember that in many situations electrical components will be case grounded. This simply means that the attaching bolts provide the system ground for the given electrical circuit.

Deposits of oil, dirt and moisture around electrical connections or terminals can provide an excellent path so that the current flows to ground.

This may also cause a grounded circuit condition. Remember that current flows through the path of least resistance in attempting to complete its circle back to ground. These three types of circuit malfunctions are things that you will find as the root cause of your car electrical problems.
You should keep this in the back of your mind when you are using a wiring diagram to diagnose suspected electrically related automobile complaints. Give this circuit malfunctions page a bookmark or share. Then watch some of my exclusive car repair videos from the links below.

Learning more about the basic theory of electricity is valuable knowledge to have under your belt. But more importantly, when you understand how it works diagnosis and auto repair becomes much easier. Learn more from me about automotive electrical.

I put together a repair video that shows you some tricks and techniques I use for quick diagnosis. See the method I was taught for the proper use of automobile wiring diagrams.People seem to like the auto repair how to videos I put together.
Here is one that shows you how to use online car repair manuals.The homepage is available from this next link. You can get a brief summary of what else is covered on this website.

The next link takes you from circuit malfunctions to auto repair advice.