vw fuse 25

autoperdu
Posts: 4
Joined: Mon Jan 25, 2016 5:19 pm

vw fuse 25

Post by autoperdu »

Hello all I am looking forward to having yet another excellent forum to search for answers and thank all who are willing to give advice in advance! But let's get onto my problem...
I own a 2001 jetta mk4 gls 2.0 and have a recurring problem, my fuse 25 keeps blowing. I have tested the interior fan and it is working fine, the resistor has continuity and for a period of time when a new fuse is put in it will work fine, all speeds of interior fan work, ac works etc.. Sometimes I may get a day out of a new 25amp fuse, sometimes just a minute... I have replaced the controls with a part from junkyard passat and that worked for a week. I feel that it is either a short somewhere or a sticky relay, I am not really an electronics guy, just another shade tree mechanic trying to get the most out of his aging car.
Any help would be appreciated!
cvergi01
Posts: 3
Joined: Mon Jan 25, 2016 9:19 am

Re: vw fuse 25

Post by cvergi01 »

This is the fun stuff. We are talking about Ohms Law here... E=I/R

E=Voltage - Battery constant
I=Amperage - Flow
R=Resistance - The higher the resistance, the less amperage that will flow. Think of a garden hose flowing water, put your thumb over the hose and create resistance, less water will flow.

We know that E = 12.6 (battery voltage)
We need to find out which part of that circuit is causing more than 25a to get pulled, popping the circuit. If you can find out the resistance value of the individual components with your multimeter, we can plug them into the formula and see what is pulling more than 25a...

In order to work out what we want, you rotate the formula...

E=I/R becomes
I = E/R

Lets say your blower is pulling 5 Ohms, I = 12.6/5 that math comes out to 2.52 amps. Not enough to pop the fuse.

Now lets say your blower is only pulling .5 Ohms allowing more current to flow through the circuit... I = 12.6/.5

This equals 25.2a. Enough to pop the fuse.

Remember to check resistance with the part unplugged from the circuit, and you have to check all the components on the circuit to get the overall draw.

I'm not very good at explaining stuff so If this doesnt make sense, here is a good explanation:

http://www.allaboutcircuits.com/textboo ... ce-relate/
gfmatthe
Posts: 12
Joined: Wed Jan 27, 2016 1:43 pm

Re: vw fuse 25

Post by gfmatthe »

Is your cabin air filter plugged? Wet? water could be getting to fan and wiring.
check resistance across all 4 speed paths on your resistor pack, and check the thermal fuse as well.
Speed 4 bypasses the thermal fuse you could be grounding out here as well. Have found water is responsible
a lot of the time.
Gary.
LudwigVan
Posts: 51
Joined: Thu Oct 08, 2015 8:26 pm

Re: vw fuse 25

Post by LudwigVan »

Thats probably a bare wire finding a short to ground and pulling that high current. Its ugly, but wire tracing is the only solution,
autoperdu
Posts: 4
Joined: Mon Jan 25, 2016 5:19 pm

Re: vw fuse 25

Post by autoperdu »

For all whom have given suggestions, thank you, in the end found that it was the fan control module located in front of the battery on the drivers side, looks like this:
vw fan control module.jpg
vw fan control module.jpg (115.92 KiB) Viewed 11046 times
Replaced and all is working as it should be now!
Thanks again for all the suggestions.
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