Hi all 

 

 Having an issue whereby the blower fuse is becoming very hot and melting the casing but not actually blowing it outright. I've checked and it's the correct fuse. Any ideas before I call in an auto electrician? 

 

My battery is abit lazy there days and will be replacing it next week before winter sets in. Possibly this but I'm not convinced ? 

 

Cheers 

John

The contacts are not gripping the fuse correctly, the more they overheat they less they grip the worse it becomes.

 

It could also be oxidisation on the fuse blade.

Replace it and clean the contacts, if it still does it then replace the fan speed resistor pack.

53 minutes ago, sepulchrave said:

Replace it and clean the contacts, if it still does it then replace the fan speed resistor pack.

Cheers sep.

Can't see how the resistor can cause the fan to draw more current that it should. It's not even in circuit when the fan is on setting 4. Do you use that setting much?

 

When did the pollen/cabin filter last get cleaned out or replaced?

50 minutes ago, Wino said:

Can't see how the resistor can cause the fan to draw more current that it should. It's not even in circuit when the fan is on setting 4. Do you use that setting much?

 

When did the pollen/cabin filter last get cleaned out or replaced?

Don't use writing 4 much no. Usually one or two. 

 

Polllen filter was replaced at the last service in February. 

Hmm, I wonder if someone has wired something else off this fuse?

1 minute ago, Wino said:

Hmm, I wonder if someone has wired something else off this fuse?

Not sure. I've had the car since 2016 and our certainly not wired anything from it in my ownership. 

4 hours ago, J.R. said:

The contacts are not gripping the fuse correctly, the more they overheat they less they grip the worse it becomes.

 

It could also be oxidisation on the fuse blade.

Whats causing them to overheat in the first place ? 

As a side note...the fuse isn't actually blowing...just melting the plastic part of the fuse and the fuse panel around it. 

14 minutes ago, Johnnynapalm said:

Whats causing them to overheat in the first place ? 

His first sentence says "the contacts are not gripping the fuse correctly "

 

That itself will cause overheating because a loose contact is a high resistance contact. Passing currents through high resistance contacts generates heat. 

 

Bend the contact pairs gently towards each other after a tickle with some superfine abrasive paper (1000 grade or more).

2 hours ago, Wino said:

Can't see how the resistor can cause the fan to draw more current that it should. It's not even in circuit when the fan is on setting 4. Do you use that setting much?

 

When did the pollen/cabin filter last get cleaned out or replaced?

 

Well, because the voltage into the resistor doesn't change but the current dissipation can increase if the resistor is failing and heating up. You do know that a resistor dissipates heat in dropping the voltage right?

But that heat is a loooong way from the fuse. 

 

2 minutes ago, Wino said:

But that heat is a loooong way from the fuse. 

 

 

What's causing the fuse to overheat is that the current draw has increased to the point where it's on the verge of blowing and the fusible link is getting hot enough to melt the plastic capsule. Either the fan motor is failing or more likely the fan resistor, guess which one is cheaper and easier to replace and has a reputation for failing?

Imagine that the resistor has failed so far short-circuit that it now presents zero resistance in series with the fan.

That's just the same as the fan being switched on at position 4, with the resistor bypassed. No more current than the fuse is specified for.

10 minutes ago, Wino said:

Imagine that the resistor has failed so far short-circuit that it now presents zero resistance in series with the fan.

That's just the same as the fan being switched on at position 4, with the resistor bypassed. No more current than the fuse is specified for.

 

So you're saying it can't be the resistor and must be the fan motor. I still think changing the fuse and using switch cleaner on the contacts will probably fix it.

But I also know that resistance increases as a component heats up.

The contacts on a fuse holder if they are gripping the fuse correctly will not overheat even if the fuse is running continuously at just under the rupture current.

 

resistors fail open circuit they dont create a short circuit and even if they did as has been pointed out the fan would just run at maximum speed.

 

Wino's advice on how to redress the contacts is spot on.

@sepulchrave My first thought was the motor; then a clogged cabin filter causing more load on the fan, but J.R.'s explanation is my favourite atm. 

11 minutes ago, Wino said:

@sepulchrave My first thought was the motor; then a clogged cabin filter causing more load on the fan, but J.R.'s explanation is my favourite atm. 

 

I've come across situations where the overheating fuse has melted the contact block as well and the contacts recede into the melted plastic making the situation worse, a symptom rather than the cause itself.

J.R. may well be correct but if it isn't that then I would go to the resistor block next rather than heading straight for the fan motor.

26 minutes ago, sepulchrave said:

But I also know that resistance increases as a component heats up.

Congratulations.

13 minutes ago, Wino said:

Congratulations.

 

Please stop.

 

I said:

 

6 hours ago, sepulchrave said:

Replace it and clean the contacts, if it still does it then replace the fan speed resistor pack.

 

To the OP, and you just went off on one.

 

Lay off the sauce, it makes you combative and unpleasant.

I just pointed out why I think the resistor couldn't be involved. You turned that into a battle by attempting to mock my understanding.

I'm not drinking this evening. I'm unpleasant? That's rich.

 

I'll try cleaning the contacts as advised with sandpaper . The block has melted abit now as well though. 😞

 

ill order a fan resistor pack anyway as it's cheap and easy to replace. 

 

thansk for the help lads....😃

Looking at this one from a technical point of view. heat is the result of  The product  of the current squared and resistance. In a perfect world, there would be zero resistance between the fuse blades and the holder and hence  no heat as the product would equal 0. (I x I x 0=0) . it's the same result as I've found on the dip headlamp connector.In one case the lamp was not lit but the plastic holder had melted .

Simple way of proving whether it's fuse or other. Measure the voltage drop from the 12v into the switch and  th + side of battery. But it could just be a dodgy fuse. Why not change it and monitor the fuse.

Why guess when you can prove it.

OP- if looking for a new battery- Euro  have some decent discounts on at present. My battery is an 096, and standard one is ( with discount) circa half what I remember paying for the last one .

 

Edited 26 October, 20196 yr by VWD

13 minutes ago, VWD said:

Looking at this one from a technical point of view. heat is the result of  The product  of the current squared and resistance. In a perfect world, there would be zero resistance between the fuse blades and the holder and hence  no heat as the product would equal 0. (I x I x 0=0) . it's the same result as I've found on the dip headlamp connector.In one case the lamp was not lit but the plastic holder had melted .

Simple way of proving whether it's fuse or other. Measure the voltage drop from the 12v into the switch and  th + side of battery. But it could just be a dodgy fuse. Why not change it and monitor the fuse.

Why guess when you can prove it.

OP- if looking for a new battery- Euro  have some decent discounts on at present. My battery is an 096, and standard one is ( with discount) circa half what I remember paying for the last one .

 

Hi......I've replaced the fuse a few times now and it's just the same. 

 

Yes I've seen the batteries on euro car parts but thanks for the heads-up anyway. 

 

I've ordered an Exide premium from eBay now for £70

 

Cheers