I thought it was initially the defective air compressor drawing too much amps but after replacing the air compressor 3 times (obtained from junk yard), it makes no difference So i left the pump disconnected and it STILL blows the fuse?.

I tried replacing the compressor relay (again obtained from junk yard) too but i cant vouch for the correct relay ..all i know was that it had Hella stamped on top but it had different part numbers. Nonetheless, i put the original relay back in and the original pump (disconnected) back in. I just need to find out what is causing the fuse to blow all the time?



2000 S430 180K Augusta, GA

 

First, you need to work on your diagnostic skills. Apparently, the fuse blew, and you changed the compressor. The fuse blew, and you changed the compressor. The fuse blew, and you thought that changing the compressor would help? Not very likely...

You need to get the correct relay - new, with the correct part number according to your VIN. You need to make certain that you are actually using 40-Amp fuses, preferably American-made. If the fuse blows with the correct relay installed and the compressor disconnected, it would seem that there is a wiring problem.

One way to approach the troubleshooting on the problem is to make a test rig. Take one of the blown fuses and locate the two tiny metal bits on the face of the fuse (next to the number). Go buy four feet of "lamp cord" or "zip cord" at Home Depot, Lowes or a similar store. This is the two-conductor wire used to connect a table lamp to the wall socket. Get a 12-volt light bulb, such as a taillight or parking light bulb. Take one of the blown fuses and locate the two tiny metal bits on the face of the fuse (next to the number). Dig down into the plastic enough to expose the metal bits. Solder the two conductors on one end of the wire to the two small bits on the face of the fuse. Solder the connectors on the other end to the base and the center connector of the light bulb.

Do the following steps exactly, completing each step before going to the next.

With the compressor unplugged and the relay removed, plug the test rig into the Airmatic compressor fuse slot. If the bulb burns, there is a short to ground in the circuit somewhere between the fuse socket and the relay socket. The test rig will allow you to safely start testing to see where the circuit is grounded.

If the bulb does not burn, turn the ignition switch ON. If the bulb burns, there is a short to ground in the circuit somewhere between the fuse socket and the relay socket. The test rig will allow you to safely start testing to see where the circuit is grounded.

Turn the ignition switch OFF.

If the bulb does not burn, plug the correct relay into its socket and turn the ignition switch ON. If the bulb burns, there is a short to ground in the circuit somewhere between the fuse socket and the compressor plug. The test rig will allow you to safely start testing to see where the circuit is grounded.

Turn the ignition switch OFF.

If the bulb does not burn, connect the compressor plug and turn the ignition switch ON. If the bulb burns, there might be a short to ground in the compressor, but at this stage the chances of that appear to be vanishingly small.

 

I appreciate the detail troubleshooting steps - but I still don't know how to solve the issue. What could be causing the fuse to blow with both the relay and compressor removed with the ignition turned on?

I am suppose to be looking for a short somewhere? I looked at the two cables going to the compressor and they don't appear to be chaffed. Incidentally, the big cable connector i assume is the power cable. The little cable connector I assume is the control wire. So if there was a short, it would be in the later cable? I am somewhat apprehensive about dismantling the fuse box to check the wiring between the relay and the fuse. That would be just creating more electrical issues.Is there anything in the SAM fuse box that could be causing problems upstream?

I measured the voltage drop between the two broken fuse pins and i measured 14V. I thought it was suppose to be 12V? Nothing registered for the current (amps).Shouldn't i be getting some amps between the two fuse legs with the ignition running...even with a blown fuse? I put a 50 Amp fuse (with no relay or compressor) and it blew with a loud pop when i turned on the ignition.

 

You have a short. If the fuse is blowing when power is applied (ignition on) and no load (pump removed) then it can ONLY be a short in the wiring. If you're not comfortable fixing a short in the wiring, then get it to a shop that can handle this.

In the meantime, hoping for an alternative explanation is unproductive.

 

To simplify...

An electrical circuit is just that - a circuit, a path. A wire runs from point A (the ignition switch) to point B (the input side of the fuse). Then the power runs thru the fuse to point C, the output side of the fuse. A wire runs from point C to point D, the input terminal of the relay, which is an electrically-operated switch, open until the relay operating coil gets power to close the relay contacts. When the relay is triggered, the contacts close, sending power to point E, the output terminal of the relay. A wire sends power from point E to point F, the input terminal of the compressor (yes, one of the heavy wires). There, the power goes to the pump motor, operating it, then to point G, the ground/earth terminal of the compressor.

If the fuse blows with the relay removed, the compressor has nothing whatsoever to do with the problem, and neither does the relay. From your description, the problem has to be at point C, point D, or the wire between them - a direct short to ground (the body/chassis) on the output terminal of the fuse, the input terminal of the relay, or the wire between. I agree that it might not be smart for you to disassemble the SAM - it may be time to call in outside help. If you do decide to disassemble the SAM, you MUST disconnect the ground terminal of the battery first.

You measure voltage from a point on the circuit to ground. You measure Amperage by breaking the circuit and inserting the meter in the circuit. At that point, the meter must be capable of passing the full current flowing thru the circuit. If you are instantly blowing a 50-Amp fuse, you obviously have much more than 50 Amps flowing thru the circuit. There are virtually no consumer-grade multimeters that will handle that much current flow, and you will instantly blow the fuse inside the multimeter (if you are lucky), or instantly destroy the multimeter. You didn't correctly measure the available current flow. The reason for using the test rig that I described is that it will allow you to see when the short is active, without allowing more than the amount of power required to light the bulb to flow, thus keeping you from melting wires or burning the car to the ground.

Twelve volts is the "nominal" automotive voltage. A good, fully-charged automotive battery will show approximately 12.6 to 12.8 vdc. With the engine running, the circuits should show 13.6 to 14.2 vdc so the battery will be charged.

 

I let the car sit in the garage for a few days. This afternoon i went to work on it and put in a used 40A fuse in and nothing else and cranked the engine and it DID NOT blow the fuse!! So i hooked everything else back up, and fired the engine up, and compressor came on!!

There is no under splash under the compressor, and since it was raining heavily when I last drove the vehicle, I can only fathom that water got in somehow and short circuited something. The fuse boxes were all dry. I am thinking water got sucked in the air hose that goes from the compressor to the filter because when i unplugged that hose several days ago, some droplets of water came out. I didn't think much of it at the time.But anyways...I am happy the compressor is working once again. I will have to go to a junk yard, and see if i can get an under-splash!

 

I'm running into a similar issue where my 40 amp looked like one end of it got burnt. We had heavy rain a few days ago as well when I drove it and my compressor stopped working. I’m hoping I can grab another 40 amp fuse and get my compressor going again. Wish me luck! Lol

 

Burnt isn't blown. It is unlikely that you have any problem with the relay or compressor.

Electrical power going thru resistance creates heat. If one leg of the fuse is just a tiny bit loose in its connector, or there is a bit of corrosion between the two, normal current flow thru the connection will generate a little heat. This heat will help create a bit more corrosion, which will create a bit more heat, which will create a bit more corrosion, which will...

You need to carefully clean and tighten the connection for the fuse. You can buy a product called Stabilant at some electrical shops on-line, etc. This stuff is expensive, but it works! You can also buy "contact cleaner", which will also help to some extent.

 

That actually helps and makes total sense! I appreciate the information! I’ll look into checking that out and giving it a shot. I was starting to worry my compressor was shot and received some misleading information but, this is the best info I’ve received so far! Thanks again!