Rear Window Defogger Problem continued..
Thread Starter
Intermediate
Joined: Feb 2003
Posts: 36
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From: Cumming GA
Rear Window Defogger Problem continued..
I thought I had a problem with the rear window defogger switch but it was OK.
I noticed slight melting around the connector in the fuse panel and that connection may be damaged. I connected a lead to the battery positive side thru a 30 amp fuse by itself to the grid and it seemed to work OK, but then the fuse started to really heat up and the plastic fuse housing started to melt. The fuse didn't blow. My manual says the grid should be about .5 ohms (12/.5= 24amps) I measured about .8ohms across the grid so its not shorted and the current should be less. Is there a special type fuse that should be used on this circuit? Since it didn't blow I'm assuming that it didn't draw over 30 amps. Does anyone have any ideas?
I noticed slight melting around the connector in the fuse panel and that connection may be damaged. I connected a lead to the battery positive side thru a 30 amp fuse by itself to the grid and it seemed to work OK, but then the fuse started to really heat up and the plastic fuse housing started to melt. The fuse didn't blow. My manual says the grid should be about .5 ohms (12/.5= 24amps) I measured about .8ohms across the grid so its not shorted and the current should be less. Is there a special type fuse that should be used on this circuit? Since it didn't blow I'm assuming that it didn't draw over 30 amps. Does anyone have any ideas?
Race Director
Joined: Oct 2002
Posts: 13,717
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From: RI
Re: Rear Window Defogger Problem continued.. (tdjordan)
I would recalculate it by 14.2/.8. 12 is with the car off, but most people run defoggers with the car on which runs 13.8 to 14.2 typically and sometimes as much as 15 on a 10 degree day. Calculations based on 15/.8=18.75 and 12/.8=15. If you are melting a 30 amp fuse something just don't sound right. Are you sure you meter is properly calibrated to measure a resistance that small? I would short the meter leads and see what the leads measure register THEN measure the grid and take the difference, that will give you the true indication of how much current is passing. It must be a very small value if its melting a 30 amp fuse. Keep us posted
Chris
Chris
Thread Starter
Intermediate
Joined: Feb 2003
Posts: 36
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From: Cumming GA
Re: Rear Window Defogger Problem continued.. (kittmaster)
I think I now have this fixed. Not really sure of the cause..Switch is OK. I cleaned the connections, rewired the connector straight from the battery with a new "good" 30 amp fuse with new connectors and every thing works fine. I even put the older "cheaper looking" fuse in and no heat up or melting of the fuse. The fuse panel does have a problem at the defogger 30 amp fuse connector and the wire connector to the panel won't release. A possible reason for the melting of the fuse could have been that I was using alligator clips to hold the fuse blades. At 30 amps the current density at the clip ends could have generated a lot of heat. Any way thanks to all for the advise.
