Contour Enthusiasts Group Archives Forums General Troubleshooting Blower fuse keeps blowing!!!

When the resistor fails it creates an open (higher resistance) path thus drawing less current (low or no fan operation). You normally would not suspect a blown resistor when looking for an over current condition. It is more likely damaged insulation (caused by heat from the failed resistor) or a bad fan motor or switch. He did state that it â�?��?only worked on high since he got itâ�?� This would indicate a failed resistor but would not cause the new blown fuse condition.

jeff

EDIT: not worth it..

suffice to say I disagree with the statements presented in this topic that state a blown resistor can't cause blown fuses.


Ray

But it is worth it,
In order to draw current you need a complete circuit. In the case of an automotive electrical system, that would entail a connection from the positive 12-volt battery terminal (supply) to the negative terminal (ground or chassis). The blower resistor is in series (on the supply side) with the blower motor. The blower motor completes the path to ground. The blower resistor creates a â�?��?voltage dropâ�?� between the motor and the 12 volt supply that causes the blower to run at a lower speed (Ohms Law, E voltage drop = I current x R ohms. By Ohms law the voltage drop creates heat at the resistor (P watts=E volts x I current). The motor will draw a set amount of current based on the applied voltage (12volt supply - series resistor voltage drop). Increasing the resistance will slow the motor and pull less current, decreasing the series resistance will speed the motor and pull more current. Even with a shorted resistor, the max current through the fuse would not reach 30 Amps. It would be the same as when the fan switch is set to high (resistor shunted â�?��?shortedâ�?� out of the circuit).

Since there is no â�?��?groundâ�?� connection on the blower resistor it cannot supply a return path for the current and cannot cause the fuse to blow. All it would do is force the blower to run at full speed all the time. Not to mention that in my more then 35 years of electronics I have never ever had a resistor fail â�?��?shortedâ�?�, even wire rounds.

What will blow a fuse is,
A bad blower motor.
Exposed wiring due to insulation damage.
High resistance on the fuse terminals causing excessive heat at the fuse.

The reason this is important is that the source of the short must be found and repaired.
I donâ�?��?�t want to read the next post saying, â�?��?I had to jump out of the car because it filled with smokeâ�?�.

jeff

Jeff,

I applud the final concensus: finding the reason for the blown fuse.

I have seen shorted resistors (albeit a wirewound one, but still) We were required to troubleshoot a circuit with one inserted as a controlled fault when going through the Naval Electronics Technicians Training School (NETTS)

While I don't have 35 years of experience, I do have 8.
I focus mainly on UHF, VHF, LF, VLF, and SATCOM transmissions (Radar propogation, and control, HF communications transceivers , etc)
I also work in Miniature and Microminiature soldering (up to 400x) through NAVSEACOM, as well as Fiberoptic termination and repair.

I will admit that I see no reason to cause the blown fuse, but think about this now: you've been doing this for years... how many times have you had a fault that you found and the words that went through your head were LITERALLY, "what in the hell"???", when you thought about WHY it happened.

It doesn't ALWAYS make sense, though we wish it would(certainly makes troubleshooting easier).

End result: this guy needs to find the problem. I won't argue that much. Can a blown resistor cause the fuse to keep blowing? it CAN, I have had it happen. though I couldn't explain it, and I won't begin to try. Can a resistor short? sure, but you wouldn't see it on any NORMAL earth day!

Good explanation of the circuit, btw, Jeff


Ray

Hi Ray,
I too have an RF and Satellite background and used to work on mil spec equipment including a demodulator used on submarines. Right now I work for a large information outfit and am mainly involved with terrestrial comms (T1, DS3, OC3) but I am working on an upgrade to our DVB Satellite feed. I keep my head in the Trons by repairing Audio amps and Pro audio stuff (and the tours electrical system).

My apologies if it seemed like my posts were attacking you directly. My concern was that this issue should be fixed by someone with an electronics background (as you would agree).

It���?�s nice to know that someone else has an RF background. I was beginning to think I was alone in the world (all my friends are PC geeks).

jeff

When your fuse blew did it also take out the L and R turn signals?

I have a fuse #23 keep blowing (15A) so i put in a 20A (i know not good to do) and it works a little while and when I put a 30A in the wiring started to smoke...

When the fuse blows i loose the blower fan and my turn signals...

I looked at my haynes manual wiring diagram and i dont see out the two circuits connect but damn if they dont both stop working if the fuse blows...

thanx..