30A fuse for fans blowing after replacing fuse box and alternator cable

[OlyTDI]

2004 Golf GL, Manual, 200K miles.

The backstory: I had the relatively common battery top fuse box melting problem recently where the 30A fuse slot for the fans over heats and melts. I bought and installed a replacement fuse box from IDParts about a month ago. I also up-sized and replaced the main alternator cable at that time -- discussions around the fuse box melting issue suggested that replacing the alternator cable is a good preventive measure in terms of lowering resistance and keeping things cooler. I should also note that I replaced both fans a year or two ago. Both fans work great currently. Oh, and I cleaned up all of the grounds under the battery box when I put in the new fuse box though they all looked pretty darn good. PNW car -- not much corrosion.

So the 30 amp fuse in the battery top fuse box that controls the fans blew today and I'm a little uncertain where to start with troubleshooting this. I replaced the fuse on the side of the road and the AC and fans operated just fine during the 20 minute drive back home. I cannot see any new melting/burning issues with the new fuse holder. AC works well and is cold. Both fans work when doing the fan test.

Since it's the 30A fuse for the fans that blew and it's slot was previously burned, should I start by checking all of the wiring to those fans? Could the alternator (or more likely) the regulator be the problem?

Open to any and all suggestions on where to start with this.

I tried to attach a photo of my fuse block but no joy. Cut/paste and drag/drop unsuccessful from PC being used to draft this post.

Thanks up front!

 

[tgray]

From a cold start, turn the fans on with the A/c and feel the wires at the connection points. If it is a bad connection it will get warm right away.
I would think it points to the fan going out. If the wires are good and connections are good that is the last part of the chain. Electric motors burn the interior coils and short out pulling more amps or it could be dragging. Put a new fuse in and turn the fans on with the A/c running. See if one motor gets real hot real quick. If a motor gets hot it will take more current and more current equals more heat. Get a good volt meter and check the voltage from ground with the fan running. First at the battery and then at the point where it goes into the fan. There should be very little voltage drop on the wire.

 

[OlyTDI]

Thanks tgray. Appreciate the tips. When you say feel the wires at the connection points, do you mean at the fan plug-in harnesses? I will do that in the morning when things are as cold as they'll get.

I would hope I'm not needing to replace fans once again! The originals lasted 17 years or so. These two are both relatively new though they were Chinese aftermarket....I couldn't get the whole frame with fans out of the vehicle without taking out my frost heater so I just removed the new fans from their new frame and installed them on the in-place original frame. Worked fine.

 

[tgray]

Yes, any connection point is where problems can happen and things may get hot. Fan plugs can corrode or the one up by the battery. I have had OK service with the china fans but the support frame is usually junk. The biggest problem I hate with the china junk is they run out of balance and vibrate too much. The original frames are way better. You can pull the bumper and front off the car without too much work and move the radiator forward to get the fans out better. I know it takes longer but sometimes I get tired of tearing up my hands to save a little time.

 

[OlyTDI]

Yes -- I did keep the OE frame and put the Chinese fans on the original frame so that's better. I think they do vibrate more though. I'll see if I can detect anything tomorrow. The problem with all of this is that if there is fuse-blowing resistance, it's only going to get worse. I keep a pretty tight ship on everything but maybe after 20 years, these cars just start to freak out a bit.

 

[Zak99b5]

May be a stupid question, but did you swap over the last (working) fuse you used from the old melted box to the new one when you changed it out, or was it a brand new fuse?

 

[Genesis]

I would not be even slightly surprised if one of the fans has an internal short; that will of course blow the fuse. The "low speed" is just a dropping resistor and it gets VERY hot when running, which of course is not so good when it comes to longevity. A PWM fan would have cost an extra $5 so neither VW or the aftermarket did that.... go figure.

 

[OlyTDI]

May be a stupid question, but did you swap over the last (working) fuse you used from the old melted box to the new one when you changed it out, or was it a brand new fuse?

If you mean the 30 amp spade fuse, no -- that old fuse was burnt to a crisp. I replaced all three of the 30 amp fuses on the new box with new 30 amp Eaton fuses. The old fuses associated with the old fuse box were either burnt or scorched as was the old fuse box.

 

[OlyTDI]

I would not be even slightly surprised if one of the fans has an internal short; that will of course blow the fuse. The "low speed" is just a dropping resistor and it gets VERY hot when running, which of course is not so good when it comes to longevity. A PWM fan would have cost an extra $5 so neither VW or the aftermarket did that.... go figure.

Any way to get at that question, Genesis? If a short, it would have to be intermittent and thus difficult to assess, I would think.

 

[Zak99b5]

Ok I was thinking that if you HAD moved the fuse from old to new box, it may have been compromised from heat, thus the failure.

In any case, when a fuse blows, I always just replace it and take a quick look for any obvious issue that might have caused it.
If the new fuse lasts, it’s all good; if it blows again, then I go hunting.

 

[OlyTDI]

Ok I was thinking that if you HAD moved the fuse from old to new box, it may have been compromised from heat, thus the failure.

In any case, when a fuse blows, I always just replace it and take a quick look for any obvious issue that might have caused it.
If the new fuse lasts, it’s all good; if it blows again, then I go hunting.

Fair enough -- it just seems odd that after replacing all of that, I blew a fuse at all. What I know it isn't, is the fuse box or fuses or grounds...l don't know if the fans are the only thing on that circuit -- I'll have to dig out the shop manual. Perhaps the compressor clutch is as well. I couldn't tell when the fuse blew but I'm pretty sure it was on startup. And it was hot out.

 

[Zak99b5]

Fan shouldn’t be drawing any current at all through that fuse at startup. Was A/C on?

 

[OlyTDI]

Fan shouldn’t be drawing any current at all through that fuse at startup. Was A/C on?

If I followed my usual routine, I got in the (hot) car, started it (cabin blower likely would have been on low), pressed AC button, then turned fan on high while driving with the windows down to vent the hot air. After a few minutes, I noticed that the blower air was hot, not cool so I pulled over and found the blown 30 amp fuse -- same one as had burned up on the previous fuse box.

 

[tgray]

Sounds like a half burned out china fan motor. Also, once the old wire was burned the low voltage may have damaged the fan motor. Motors do not like running on improper voltages. The fan may have not had enough power to turn enough and cool itself and just soaked up the power burning everything out.

 

[OlyTDI]

Interesting. I wouldn't have thought that a motor could half burn out. And then go on to operate for a couple of years. Maybe there's just enough heat generated that on a really hot afternoon, it's all put over the top.

 

[OlyTDI]

Update: So I did start the vehicle from cold today and set the cabin blower to the lowest setting. About 3 seconds after I pushed the AC button, that 30A fuse blew. Both fans started but never got up to speed. While the engine was running and with the cabin blower and AC still on, I inserted a fresh 30A fuse and it blew as soon as I inserted it.

Nothing got warm enough to detect.

Don't both of those fans come on for engine cooling even if not using the AC? I'm trying to figure out how to test the fan startup vs the AC clutch actuation as the source.

When my original fans died (actually only one but replaced both), there was no shorting or blown fuses. It just wouldn't work (but would for a bit if I banged on the motor).

Is the prudent approach to just replace the fans again?

 

[J_dude]

Is the prudent approach to just replace the fans again?

Maybe grab one from the pick-n-pull?

 

[csstevej]

You have a dead short…..nothing is gonna heat up in the time the fuse blows.
Disconnect one fan at a time and try turning on the ac….if it blows disconnect that fan and try again to isolate issue.

 

[OlyTDI]

You have a dead short…..nothing is gonna heat up in the time the fuse blows.
Disconnect one fan at a time and try turning on the ac….if it blows disconnect that fan and try again to isolate issue.

that makes complete sense.

 

[OlyTDI]

07/02 PM update:

I did what csstevej suggested. I tried each fan independently by disconnecting one at a time and ran each with engine off and cabin blower on and AC switch on. Each worked fine -- no problems, no fuse blowing. I then reconnected both fans and repeated the test with both fans on. Everything worked great. I'll add that the fans, the wiring, the connection pins -- everything looks clean and without a hint of corrosion.

Then I started the vehicle, and at idle turned on the cabin blower and activated the AC switch and the fuse instantly blew. So it seems that whatever is different in those activities when the engine is running vs not running is where the problem lies. That would have to be the activation of the AC compressor would it not? Any ideas on next steps?

Something with AC startup with engine running is at play here.

Thanks everyone for helping out thus far!

 

[J_dude]

That would have to be the activation of the AC compressor would it not?

I’m not sure, whether the car is running or not shouldn’t affect the activation of the AC clutch, it’s just an electro-magnet coil.

 

[OlyTDI]

I’m not sure, whether the car is running or not shouldn’t affect the activation of the AC clutch, it’s just an electro-magnet coil.

Well, the AC doesn't operate with the engine not running so I would assume that when the engine is running, the compressor clutch kicks in.

 

[Zak99b5]

Unplug the clutch coil and try again. The plug is clipped to the compressor body.

 

[J_dude]

Well, the AC doesn't operate with the engine not running so I would assume that when the engine is running, the compressor clutch kicks in.

Yeah but if the key and the AC switch are on the coil will be energized. The AC only doesn’t operate because the compressor has to be turning.
Try what Zak suggested though.

 

[OlyTDI]

Unplug the clutch coil and try again. The plug is clipped to the compressor body.

Thanks Zak995b. I just did as you suggested: disconnected the compressor clutch coil harness, engine running, blower fan on, hit the AC button and yes, it blew the fuse instantly. That now removes the compressor clutch coil and the fans from the equation.

 

[OlyTDI]

Yeah but if the key and the AC switch are on the coil will be energized. The AC only doesn’t operate because the compressor has to be turning.
Try what Zak suggested though.

Good to know!

 

[OlyTDI]

So there is a short somewhere between that 30A fuse tray, the AC switch and the clutch coil harness connector. I'll start visually inspecting from that coil connector back but most of that wiring harness is completely covered.

I'm going to run out of 30A fuses!

 

[Zak99b5]

Maybe start looking by the FCM. Wires behind the dash seem less likely to be bad.

 

[OlyTDI]

Maybe start looking by the FCM. Wires behind the dash seem less likely to be bad.

Roger that. Starting to work from that battery to fuse box.

 

[P2B]

Maybe start looking by the FCM. Wires behind the dash seem less likely to be bad.

Even if they were bad, they would blow the 5A fuse by the driver's door, not the 30A under the hood. AC switch is just an input to the FCM which does the high current switching.