Rear Defrost

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  #1  
Old 07-28-03, 04:23 AM
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Rear Defrost

My wifes been bugging me for about 3 months now to fix the rear window defrost. A while back I checked fuse and it's ok, when you turn it on the light comes on indicating it's on. When I washed it last I looked over the element on the window and it looks good "no breaks and both connections are plugged in".

My next step I guess is to confirm voltage at the element. Do I check from plug to plug or 1 plug to ground? What voltage should I get? Do they send 2 hot legs or just 1 wit ground at other plug.

94 Chevy disposable. I mean Corsica. V6/W/air/auto.
 
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  #2  
Old 07-28-03, 05:23 AM
Joe_F
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It may be a break at the bus bar connection.

I'm not sure I understand the problem. Does the rear defogger work at all (can you see that it's defrosting at parts of the window)?

If parts are defrosting and others not, that's a break in the grid.

If nothing is defrosting, I'd check the bus bar connection for breaks. It's common they break there.

The dealer has a rear window defogger repair kit as do some parts stores. Follow the directions to a T. If not, have a glass shop handle the break for you. Mark it with a crayon or grease pencil so they know what you've found.
 
  #3  
Old 07-28-03, 06:37 AM
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I would test both side of the element running through the back window for continuity before anything else. If you have a continuity tester you should put one probe on each end. If you find no continuity go to the middle and see which side is good and which is bad. Continue this until you localize where the break is. I remember that 3M makes a product that can be painted on the window that will conduct electric so the defroster will work once again. Make sure the defroster is off, no current. when doing the continuity checks.
 
  #4  
Old 07-28-03, 05:27 PM
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Bus bars look good. Everything looks great physically.
It don't defrost at all.
I will check continuity tomorrow but what about checking the voltage at the plugs at the window itself?
 
  #5  
Old 07-28-03, 06:11 PM
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one side will be power the other side will be ground you can check voltage from side bar to side bar should be about 12 volts.
 
  #6  
Old 07-28-03, 06:11 PM
Joe_F
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The grid could still have a break at the base or somewhere common.

This is where a service manual is handy---they have the complete diagnostic and repair procedure there.
 
  #7  
Old 07-29-03, 07:27 PM
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Checked continuity and it was fine checked volts found none. Double checked the fuse and 30 amp breaker and all was fine.
I then removed the top part of the dash to gain access to the switch and foud the plug melted and circuit board damaged.
I cut and stripped the wires for the defrost and jumped them with heavy gauge jumper. Turned the key on and got voltage to the defrosters.
Problem arose though. after a couple of minutes the breaker tripped. Got out my handy Fluke and did amp draw and was 22.6 amps dc. The breaker is 30 amps and according to the fuse panel cover the only thing on the breaker is the defrost and power locks. Why would the breaker be tripping at 22.6 amps? Guess I should do an amp draw at the breaker?
 
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Old 07-29-03, 07:35 PM
Joe_F
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Swap out that 30A breaker for another one and try again. I have seen those go bad and cut out earlier than they should.

Barring that, something's shorted of course or drawing too much juice. Anything in Alldata?
 
  #9  
Old 07-30-03, 04:31 AM
redneck
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Funny, I had the exact same problem on a '91 beretta--just learned to live without the defroster!
 
  #10  
Old 07-31-03, 04:21 AM
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Originally posted by redneck
Funny, I had the exact same problem on a '91 beretta--just learned to live without the defroster!
If was mine I wouldn't have bothered past the fuse but it's my wifes and everyday I here about it.
 
  #11  
Old 08-04-03, 06:19 PM
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Fixed "I guess"

Went to my favorite pick & pull for defrost/wiper switch and plug harness that was burnt up. Replaced it and checked amp draw 23.4 amps dc. Let it run for a while and breaker got hotter and hotter then tripped. Pulled breaker put in a jumper to check amps at breaker 25.5 amps dc. Installed new breaker and seems fine now. Disassymbled old and it was blue from the heat build up.

Thanks All.
 
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