1987 Chrysler Le Baron Fusible Link

Hi anagy007. Welcome to the forum. The original fusible link was a special wire that was the "weak link in the chain" and would burn open before the rest of the wiring harness was damaged. It was made with special insulation that will not burn. The other characteristic is it takes a while for the wire to melt. That short time period allows it to withstand the current surge caused by the fan motor starting up. Those fuse link wires are available from the parts stores. They are purchased according to color, and one can be cut in half or three pieces to make multiple repairs.

It seems a 30 amp fuse should withstand the startup current of a fan motor, but there's an easy way to check. Unplug the new fan motor, then install a much smaller fuse, say a 10 amp for example, and drive the car for a few days. If that fuse blows, something else on that circuit is the cause. I can give you one example that pertained to a newer Caravan. When the engine rocked when shifted to reverse, the fuse link for the radiator fan motor blew leading to engine overheating. After a lot of testing, it was discovered the backup lights were on the same circuit. The wire for the backup lights had rubbed through causing the fuse link to blow. The two circuits were tied together because most people would not know when the backup lights were not working, (a potential safety concern for other people), but you would notice engine overheating.

If your smaller fuse still blows, we have to figure out what else is on that circuit. If the fuse does not blow with the fan disconnected, there may be no other problem than it needs the slow-reacting fuse link wire instead of the fast-reacting fuse. A self-resetting circuit breaker can also be installed in place of the new fuse. One common value is 30 amps.

Caradiodoc

Yup. 40 is too big. 14 gauge wires can safely handle 15 amps. The fan motor can safely draw a little more at startup, but that surge only lasts for one or two seconds. That is enough time to blow a regular fuse but not a fuse link wire.

I suspect there is some other problem if a 30 amp fuse is still blowing. Follow that circuit to see what else it feeds. If you can't find anything in the wiring diagram, I'll search for a service manual and see what I can find.

Caradiodoc

Dandy. You can get away with unplugging the fan if you use the AC at highway speed. If the fuse still blows, I would look closely at the wiring near the compressor clutch first. The magnetic coil could be shorted too, but intermittent problems are more likely to be caused by rubbed-through wires than the coil itself.

Caradiodoc

Nope. Unless I'm missing something, the two should be independent of each other. The only exception would be if the Engine Computer detects the open circuit to the fan motor, but in that time period, it only detected an open circuit for the coil part of the relay, not the high-current side.

I had a similar situation with my '88 Grand Caravan. A former student mistakenly left the fan motor's ground wire off when replacing my starter. I didn't notice it for a couple of years because all of my driving was on the highway. What little I used the AC, it still worked fine.

Now, just so I'm clear, you're talking about unplugging just the fan motor, not removing the relay, right? Have you ever noticed if that fuse blows when you are NOT using the AC? I suspect it will not because both the fan and compressor are turned on with relays so any short should be out of the circuit if the AC isn't turned on. Also, since the system worked for 2 days with a 30 amp fuse, it suggests the compressor clutch does not have a dead short although it could be intermittent. I have a trick that can tell if that is the case, but it involves running a pair of wires into the passenger compartment and connecting a light bulb. It will tell you when a short occurs, but not exactly where. Also, it means driving without air conditioning.

If it becomes a constant dead short, my light bulb trick helps in locating it too.

Caradiodoc

Here's a trick I learned as a tv repairman and used often as a mechanic. Remove the fuse and plug in a pair of spade terminals. Use two pieces of wire to connect those terminals to a 12 volt light bulb. When the short circuit appears, the bulb will be full brightness, and when you do something to remove the short, the bulb will go out, or it will dim if there is something else in the circuit such as a motor or another bulb. You may be able to make the short show up by wiggling wiring harnesses, turning parts, or banging on the body with a rubber hammer. This works especially well for screws for sill plates run through harnesses, wires crushed under the rear seat brackets, frayed and touching wires between door hinges, even corrosion between adjacent pins in a connector.

The bulb you use should be chosen for the circuit you're using it in. A brake light bulb (for a test light) will only allow about 1 amp of current to flow. If you're looking for a short in the brake light circuit, for example, when the short is gone, the test light and brake lights will split the 12 volts from the battery. That means the test light will be dim and so will the brake lights, but both can be observed to see when the short comes and goes. This saves constantly popping fuses.

In high-current circuits, those little bulbs aren't as effective because the normal circuit components draw so much current, the test light will normally be pretty bright. The slight change in brightness when the short appears is so subtle, it can be hard to see. This is where a larger bulb such as a head light bulb works best. When the short is gone, the circuit will get enough current to work somewhat. The fan motor will try to run but it will run slow. When the short appears, the bulb will be full brightness, the fan will stop, and current in the circuit will be limited to a safe 5 amps by the bulb.

There's a twist though to this trick. For it to work with your new fuse holder, the engine will need to be running, the air conditioning will have to be turned on, and the Engine Computer will have to be willing to turn the two relays on. And, the short could be in either the fan circuit or the compressor clutch circuit. An alternative to this is to put the fuse back in and use the test light in place of the relay contacts. This will power up the circuit without even needing to have the ignition switch turned on. Those same spade terminals can be used in the relay connectors. Each connector will have four wires. The two for the relays' coils will be small, typically 14 gauge or smaller. You want to connect to the two larger wires.

Doing this will allow you to power up one leg of the circuit at a time and the bulb will limit current so the fuse won't blow. The compressor clutch will most likely not engage because current will be too low to make a strong magnetic field, but the fan motor will probably try to run but it will be real slow. You will see the bulb go out when the fan motor or compressor clutch are unplugged if the circuit is working properly. When there is a short circuit, the bulb will stay bright even wheh those items are unplugged unless it IS one of those items that's shorted. You replaced the fan motor already so chances are it is ok. The compressor clutch could be shorted, and it could be intermittently shorted, but intermittent shorts occur more commonly from bare wires rubbing on bare metal.

Caradiodoc

Nope. You don't have to wait for the engine to cool before replacing the fuse.

Another way to approach this is to unplug the fan relay OR the compressor relay and connect the two fatter wires in the plug with a piece of wire or a stretched-out paper clip. One of those two circuits will make the fuse blow. At least we will know which circuit has the problem. The time to do that is when the fuse blows right away which sounds like when the engine is warmed up.

When the short is present, there will be nothing to limit current so the fuse blows. Instead of using that piece of wire in the socket, I'm suggesting using a light bulb. The bulb will limit current, similar to squeeing a garden hose with your fist. Your fist adds resistance to the flow of water, (current), but enough water still flows to let you see where the hose is leaking, (shorted). The only difference is with electricity, you can't SEE it leaking. You have to isolate the leak by disconnecting things until the leak goes away. In this case, you can tell when the leak goes away by the test bulb becoming dim.

I know this sounds complicated but it's really very simple. So simple, most people never think of it as a valid form of troubleshooting. It is WAY easier to explain to students who have had a basic electrical class already, and when you can watch their facial expressions. As an instructor, I could tell when to continue with the explanation, and when to slow down or back up. Without those observations, all I can do is type the whole procedure. The problem with that is I've done it so many times, I start to cut corners and condense the story. Don't worry about it being "over your head". It would be easier to understand after you knew basic electrical. Most people in the automotive industry learn best by observing, manipulating, and disassembling. They do not learn well by visualizing which is what must be done with electrical. I can relate anything electrical, (which you can't see), to something related to water, (which you can visualize), hence, the fist around the garden hose equates to the light bulb in the circuit. Both add resistance to the flow of water / current.

I'm really leaning toward the compressor clutch since you're already replaced the more likely suspect, the radiator fan motor. When the fuse is blowing on a regular basis, unplug the compressor, then see if the fuse continues to blow, (or the test bulb continues to get bright). If it does, something else is causing the short besides the clutch coil.

Caradiodoc

Nope. Can't be caused by the belt itself. The fuse has no idea if the belt is slipping or even missing completely. What is likely happening is the clutch coil is partially shorting and loosing strength due to missing part of its magnetic field. That will let the clutch slip when the compressor is under load.

I realize you don't have all the fancy test equipment, but what I would do next would be to connect an ammeter's inductive pickup probe around the wire going to the compressor clutch, remove the compressor relay, and replace it with a jumper wire to activate the circuit with the engine not running, then watch the ammeter reading for a while. Wiggling the wire harnesses would show a bare and grounded wire as a fluctuating meter reading. If the current started to increase on its own without me doing anything, that would point to the insulation breaking down on the clutch coil wiring.

Caradiodoc