What makes a solenoid mess up?

Answer 1

A solenoid is a heavy current switch operated by a separate, and comparatively low current circuit. The contacts (any or all - primary or secondary) on the solenoid could be damaged or corroded. There could be a break in the operating coil of the solenoid (though this is unlikely). The solenoid plunger (armature) might be stuck or hanging up (though this is unlikely as well). Lastly, the solenoid, because it is a high current switch, may have suffered severe or permanent damage to its contact surfaces, which is one of the main reasons they fail. (This is "internal" damage and cannot generally be repaired, necessitating the replacement of the component.) Let's look at that last thing. Imagine two coins like dimes or nickels (or even quarters). Set them on one another. These are your switch contacts. Imagine the bottom one is fixed to a "base" and has a heavy wire coming off underneath it. Imagine the other coin fixed to a rod of copper or brass, and then having a heavy cable coming off the end of it. Now picture the rod of copper or brass sliding in a tube so that when the rod moves up a bit, the coins (the contacts) are apart. Install a small spring to hold it up away from the bottom coin. Crude, but effective. The rod is the plunger, and it is spring loaded to pull away from the fixed coin on that base thingy when it isn't "told" to push down and allow the coins (the contacts) to touch one another. The external circuit tells the rod to move and push the contacts together to "make" or "complete" or "switch" the circuit. The problem here is that when the contacts come together, a lot of current flows to drive the starter motor. (The ignition key just powers up the solenoid. We would have a difficult time indeed making an ignition switch that actually directly closed the switch that energized the starter - lots and lots of current - big switch.) Actually, the problem isn't that a lot of current starts to flow when the switch shuts, it's when the switch opensthat we have difficulty. Let's check that out. When a "loaded" switch (one handling current) opens, as the contact begin to move away from each other, the electricity (the current, which is driven by voltage) becomes "unhappy" about the deal. Sure, the switch opens quickly, but electricity moves at about the speed of light here, so a "fast" switch takes all day to open up from the point of view of the electricity. Anyway, as the switch starts to open, the integrity of the current path starts to disappear, and an electric arc will form. This arc is extremely hot, and the current flow that continues for the brief interval as the contacts come apart will carry away some of the superheated material out of which the contact is made. As the contacts become more damaged, it accelerates the process of degradation. Eventually the contacts in this (or any other) switch will be eroded and "burned" into ineffectiveness. Or it could be something else entirely. If you've powered up the solenoid and you have a good battery and good contacts at the terminals of the battery and on the solenoid and starter, you should hear the solenoid "click" when you hit the key. This will be followed right away by the starter starting. If all is well and the solenoid "clicks" without engaging the starter, you know the coil in the solenoid is good and there is probably something wrong with the contacts, but you'll want to double check and triple check all your heavy cables and battery, just like has been suggested to you in other posts. At some point you'll probably opt to "jump" the solenoid to see if the starter will respond to bypassing that switching action of that solenoid. If the starter cranks, your solenoid is shot. But you'll need to insure you have a solid "12 volts" at the solenoid operating terminal when you hit the key. Some mechanics bypass the key (and the associated ignition components in that circuit - hint, hint) by using a test lead with a little plunger switch in it and two clips on the ends. They will connect one of the clips from this switch to the "hot" side of the solenoid operating (activating) circuit, and then other one to the battery "12 volt" terminal (on the battery or just on the starter where the battery lead comes down). Then they just "thumb" the switch and see if the solenoid powers up, and then in turn powers up the starter. It's about the simplest test in the world. *Note: Be smart about this and think it through. Safety is the most important issue when doing any work on a vehicle (or just about anything else). Good luck.