Blowing Fuse

[RBBailey]

The 10 amp fuse for the fan has blown twice now.

When I first installed the fan, it was apparent that the low setting didn't work, but high seemed fine, and the fan runs well. So I decided to worry later about getting the resistor changed out, so that I could have defrost over the winter months.

At first, I noticed that my temporary switch, was getting too hot. So I got a 20 amp Carling, and this too got warm, but nothing concerning. When I finally found an original type switch, the heat at the switch went away completely. However, now there is enough heat at the fuse to cause it to burn out with some use. It does not blow for some time. I don't use the fan a lot, so it's hard to say.

I know that it is heating up because when this last fuse blew I put a 15 amp fuse in place and felt for the heat as I let the fan run. In about 1-2 minutes it is quite hot on one end of the fuse.

So.... this is a switched ground. The wiring seems all good. The fan itself makes no odd noises, and blows strong right away.

What should I do?

 

[Red90]

Get a new fan.

 

[RBBailey]

Interesting. Wonder if a rebuild would be worth it.

 

[Red90]

They are cheap. No need to spend any time on it.

 

[ezzzzzzz]

Run the 'new' fan load through a relay. Switches last a long time without that current load.

 

[RBBailey]

Yeah, I thought of that, right now it is stock wiring. If I have to buy a new fan, that's fine, I guess $100+ is not bad. I just don't want it to be something else, get the fan, still have the problem.

BTW, am I remembering correctly.... is there an alternative part for this?

I did buy a relay just today to complete the harness for my engine fan.

 

[RBBailey]

...The fuse box label in the cab says 10 amps... However, a workshop manual diagram shows 20 amps.

I went out to double check what I read in the truck, and it does say 10 amps, however, there is a separate set of fuses listed for the A/C unit that this truck originally had. This shows the radiator fans icon at 17 amps, and then there is a second fan icon that shows 30 amps.

 

[RDavisinVA]

Many years ago when working at the dealership had a similar scenario where a vehicle kept blowing a 10 or 15 amp fuse (don't remember exactly which).
Am older mechanic in his late 50s or early 60s would give a lot of advice to us younger guys, so I asked about the fuse.
He said put a 30 or 40 AMP fuse in and move on.
I brought up that if the wiring were rated for lower amperage wouldn't that cause an issue?
He then asked me what happens when a 10 or 15 AMP fuse shorts out?
I said it blows.
He then said what happens when a 30 or 40 AMP fuse shorts out?
I said it blows.
He said explain to me the difference.
I said there isn't any.
Then he said put in the 30 or 40 AMP fuse and move on.
I then examined the wire in a 30 Amp fused circuit and in a 10 Amp circuit and the wire was the same gauge back then.
It fixed the problem.
I remember seeing the vehicle years later and the higher rated fuse was still in place and all was operational.

Now that that's out of the way.
Run a 12V relay to take the load off the switch so you don't burn the contacts in and cause overheating conditions.
Poles: 30 Brown (+) from the hot lug on the starter
85 (-) earth
86 (+) switching means
87 (+) to appliance - in this case a fan.

Why don't you run a thermo-switch if this is for a cooling fan on the radiator?
Then the fan will run automaically.

 

[RBBailey]

Oddly enough, a retired electrical engineer just told me the same thing.

And it makes sense — if the fuse is for smaller amperage, the fuse itself would be the thing causing the high heat, causing it to blow.

I’m going to try it, but I will also be testing the heat at the fan and other places to make sure it isn’t some other problem.

This is the stock heater fan. I am putting my own cooling fan in place as well. I’ll be putting an automatic switch in.

 

[RBBailey]

I'm not seeing any heat difference at all from 10, to 20, to 30 amps. The blower motor is running cool to the touch, and only barely gets a bit warm after 5-6 minutes of running on high.

Out of curiosity, I turned on the head lights to see what kind of heat was generated at those fuses -- they also got quite hot after a few minutes.

So, would someone do me a favor and run their fan for a minute or two and see what kind of heat they feel on the ends of the fuse? I’m curious about what type of heat is normal.

Maybe 10 amps is just low enough that it burns out after a while with the natural heat that is produced. Or maybe I need a new fan, even if this one seems to be fine.

 

[RBBailey]

Ryan reports to me that his fuse is showing about 150 degrees after operating for a few minutes. The tap water at my house is 130 degrees, and that feels pretty hot to the touch. I don't have any reliable way of actually measuring the temp on the fuse though.

He also pointed out to me that the English type of glass fuse is different than the buss fuse type we have here... I hadn't known this. So when I report that I had a 10 amp fuse in place, technically, that's the same as a 10 amp buss type of fuse, but the English type would have a dual rating pushing it up to 20 amps.

It is odd to me that the other fuses are also getting hot.... makes me worried.

 

[RBBailey]

To add to the last post. I have another report of 80 degrees while running a 15 amp fuse on same circuit.

 

[RDavisinVA]

An electric motor will draw as much current as it needs to maintain the rotation of the armature.
If you don't believe me spin one up and then disconnect and connect the (+) 12V current while the motor is slowing down while measuring the amperage draw.

If the motor is getting old, worn, stiff, whatever, it will draw the needed amperage to maintain rotation.
Your best option may be to replace the fan motor.

 

[Red90]

As I tried to state. You need a new motor. These should never blow the fuse. I?ve had them seize up solid from mud and have the power left on for days without the fuse blowing or hurting the motor. Putting in relays or larger fuses are bandaids.

 

[RBBailey]

Yeah, I believe you, I just need to check all possibles. I bought the motor when I bought the engine, used, but still sucks to know how little use I got from it. Since it blows strong, the burnt out fuse was my first indication that anything might be wrong.