Found Repair For The Rear Defroster Cutting Out
01-19-2014, 04:46 PM
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Found Repair For The Rear Defroster Cutting Out 
I have had my 2002 Z28 B4C Ex Highway Patrol Interceptor since June of 2007. Right away I found the rear defroster always cycled too quickly, about 5 minutes in stead of the time posted in the manual. I took resistance readings and voltage readings and found the 30 AMP delay action breaker is under-rated by almost 4 amps. I got a set of 35 amp fuses from flea-bay (China flea-bay supplier was only place to get them), and plugged one into the place of the circuit breaker, PROBLEM SOLVED! I have the service manual set, and verified the wiring to the defroster grid was ample to handle the 34 amps needed for the grid. So, your defroster cutting off before the window is clear? Swap that 30 amp breaker for a 35 amp fuse, and you'll be fine from then on. I had done this years ago, and have not had a problem since. 
01-19-2014, 05:07 PM
#2
Better to swap the 30-amp circuit breaker for a 30-amp fuse. Using a fuse of a higher rating than the circuit is designed to handle is just asking for a day when you could turn your car into a charred heap. This is especially true of resistance based circuits like the rear window defogger. It is very common for those circuit breakers (both DEFOG and WINDOWS) to trip early as they get older but that's no reason to replace with greater amperage - that's just bad advice.
01-19-2014, 08:01 PM
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Better to swap the 30-amp circuit breaker for a 30-amp fuse. Using a fuse of a higher rating than the circuit is designed to handle is just asking for a day when you could turn your car into a charred heap. This is especially true of resistance based circuits like the rear window defogger. It is very common for those circuit breakers (both DEFOG and WINDOWS) to trip early as they get older but that's no reason to replace with greater amperage - that's just bad advice.
Thanks for the post BUT you should know I have a degree in industrial electronics and 47 years in electrical/electronics background. I have tested and verified the wiring (traced each wire size in the 2002 Camaro factory service manual) to be of sufficient capacity to handle the additional 4 amps. Also, you advised to put a 30 amp fuse in place of the circuit breaker, that is BAD ADVICE as this will result in the fuse immediately blowing because the current in the circuit is in excess of the 30 amp fuse rating. The circuit breaker is designed to absorb some overcurrent, the fuse (at 30 amps) is not. Recheck your general electrical advice and please re-read my original post. The 35 amp fuse will handle the 34 amp current flow and the wiring is of sufficient size to handle the current. It has been working correctly for years, and no toasted car!
01-19-2014, 08:20 PM
#4
Sorry, I have nearly identical education and years of experience and I still don't agree with you. If you know as much as you claim, you would know that a standard ATO type fuse will handle as much as 10% overcurrent for as long as four hours without blowing so your comparison to a circuit breaker is meaningless.
If your defogger is drawing more than the rated 30 amps, you need to find out what is wrong with it. The overcurrent capability of fuses and circuit breakers is there as a buffer to prevent blowing for short periods of excess draw... NOT to be used as a regular condition. You don't design a 35 amp circuit to run with 30 amp circuit protection - whether fuse or circuit breaker - and GM did not do so with the defogger. Since that circuit breaker protects both the defogger and the power seats, running more than 30 amps for the defogger means that the seat motors would be unusable while it was on. I can assure that is not the case - I have used the defogger and the seat movement at the same time both with the stock circuit breaker and with a 30 amp fuse when the circuit breaker was replaced due to age.
Besides, even if you have checked as carefully as you suggest and it might be safe in this one isolated circumstance, it's still bad advice for the 95% of readers here that don't understand the intricacies of circuit protection and will just figure it's okay to use a bigger fuse. Always know your audience.
If your defogger is drawing more than the rated 30 amps, you need to find out what is wrong with it. The overcurrent capability of fuses and circuit breakers is there as a buffer to prevent blowing for short periods of excess draw... NOT to be used as a regular condition. You don't design a 35 amp circuit to run with 30 amp circuit protection - whether fuse or circuit breaker - and GM did not do so with the defogger. Since that circuit breaker protects both the defogger and the power seats, running more than 30 amps for the defogger means that the seat motors would be unusable while it was on. I can assure that is not the case - I have used the defogger and the seat movement at the same time both with the stock circuit breaker and with a 30 amp fuse when the circuit breaker was replaced due to age.
Besides, even if you have checked as carefully as you suggest and it might be safe in this one isolated circumstance, it's still bad advice for the 95% of readers here that don't understand the intricacies of circuit protection and will just figure it's okay to use a bigger fuse. Always know your audience.
01-19-2014, 08:41 PM
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Sorry, I have nearly identical education and years of experience and I still don't agree with you. If you know as much as you claim, you would know that a standard ATO type fuse will handle as much as 10% overcurrent for as long as four hours without blowing so your comparison to a circuit breaker is meaningless.
If your defogger is drawing more than the rated 30 amps, you need to find out what is wrong with it. The overcurrent capability of fuses and circuit breakers is there as a buffer to prevent blowing for short periods of excess draw... NOT to be used as a regular condition. You don't design a 35 amp circuit to run with 30 amp circuit protection - whether fuse or circuit breaker - and GM did not do so with the defogger. Since that circuit breaker protects both the defogger and the power seats, running more than 30 amps for the defogger means that the seat motors would be unusable while it was on. I can assure that is not the case - I have used the defogger and the seat movement at the same time both with the stock circuit breaker and with a 30 amp fuse when the circuit breaker was replaced due to age.
Besides, even if you have checked as carefully as you suggest and it might be safe in this one isolated circumstance, it's still bad advice for the 95% of readers here that don't understand the intricacies of circuit protection and will just figure it's okay to use a bigger fuse. Always know your audience.
If your defogger is drawing more than the rated 30 amps, you need to find out what is wrong with it. The overcurrent capability of fuses and circuit breakers is there as a buffer to prevent blowing for short periods of excess draw... NOT to be used as a regular condition. You don't design a 35 amp circuit to run with 30 amp circuit protection - whether fuse or circuit breaker - and GM did not do so with the defogger. Since that circuit breaker protects both the defogger and the power seats, running more than 30 amps for the defogger means that the seat motors would be unusable while it was on. I can assure that is not the case - I have used the defogger and the seat movement at the same time both with the stock circuit breaker and with a 30 amp fuse when the circuit breaker was replaced due to age.
Besides, even if you have checked as carefully as you suggest and it might be safe in this one isolated circumstance, it's still bad advice for the 95% of readers here that don't understand the intricacies of circuit protection and will just figure it's okay to use a bigger fuse. Always know your audience.
Respectfully disagree with your 10% overcurrent with a fuse. As a spike it'll handle that, but any more than its rating and it will blow. Look, I have read many comments over the years about those defrosters not working properly, and I am sure it was a windfall for GM parts departments, but the fact remains the system was designed incorrectly. Take your own VOM and check the grid resistance, then take the voltage at idle and 2000 rpm. Use your Ohms Law table and see exactly why the breaker trips after a period of time. Its not too complicated, and only takes 5 minutes to do. The numbers don't lie, and the wiring in the car easily handles the load. I am one of the safest people around when it comes to car or any other repairs, and would not do any project that would jeopardize anyone. If a short happens to occure on the plus side, the 35 will pop just as easily as the 30. 
01-19-2014, 09:41 PM
#7
Well yes, the circuit breakers in the car's fuse panel are not much different from thermal turn signal flashers in operation. They have a bi-metal strip that is designed to curve away from the output contact when sufficient current flow causes enough heat. They are self-resetting because after tripping they cool and the metal strip again contacts the output contact completing the circuit again. They were designed that way specifically for headlights so that over-current conditions would give you flashing lights rather than no lights at all.
As the circuit breakers get older, they become more sensitive to heat causing circuit breaks with less current (i.e. less heat) as well as causing issues with high ambient temperatures.
As the circuit breakers get older, they become more sensitive to heat causing circuit breaks with less current (i.e. less heat) as well as causing issues with high ambient temperatures.
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01-19-2014, 09:53 PM
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Hi Daniel, yes it is heat related, and current related. After replacing the one that was in the car (thinking it was weak over time) it did exactly the same thing. I then troubleshot the wiring and grid and found out why it was prematurely tripping. Swapping the 30 amp circuit breaker with a 35 amp fuse solved my problem completely. So your post was right on, it is an overcurrent that heated the breaker beyond its tolerances causing it to trip before its cycle completed.
01-20-2014, 06:15 AM
#9
You should pursue logic at a more fundamental level. What has changed to the wiring since the car rolled off the assembly line? Are you really discovering something new here that GM's engineers didn't know and they didn't catch during testing of the car? Do you think GM gave us these cars with a defogger and power seat that trip off early? Is there a left wing conspiracy to manufacture cars with undersized circuit protection? Why don't you just replace the part that broke with the same thing (which worked from the factory and will work now) and move on to the next thing that breaks?
Had you done a search and read all the other threads on this, you could have learned something and not gone through all the trouble to "calculate" yourself in to a problem.
01-20-2014, 06:52 AM
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If you cut open the old breaker, you'll give yourself a more advanced education. The insides char, and the thing wears out. A new 30A breaker will make you as good as new.
I didn't graduate from MIT, but I learned somewhere along the line that 34 is less than 35.
This is some of the worst advice I've ever seen on this site. I personally prefer to replace the breaker since fuses are faster acting, but replacing the breaker with a fuse of the same rating is perfectly safe. The only downside to that is the fuse might blow. In this case, you are advising people to install a breaker that takes more amperage than the manufacturer says is safe and more amperage than you personally calculated above is safe. Doing this could overheat the wiring or cause a fire.
You should pursue logic at a more fundamental level. What has changed to the wiring since the car rolled off the assembly line? Are you really discovering something new here that GM's engineers didn't know and they didn't catch during testing of the car? Do you think GM gave us these cars with a defogger and power seat that trip off early? Is there a left wing conspiracy to manufacture cars with undersized circuit protection? Why don't you just replace the part that broke with the same thing (which worked from the factory and will work now) and move on to the next thing that breaks?
Had you done a search and read all the other threads on this, you could have learned something and not gone through all the trouble to "calculate" yourself in to a problem.
I didn't graduate from MIT, but I learned somewhere along the line that 34 is less than 35.
This is some of the worst advice I've ever seen on this site. I personally prefer to replace the breaker since fuses are faster acting, but replacing the breaker with a fuse of the same rating is perfectly safe. The only downside to that is the fuse might blow. In this case, you are advising people to install a breaker that takes more amperage than the manufacturer says is safe and more amperage than you personally calculated above is safe. Doing this could overheat the wiring or cause a fire.
You should pursue logic at a more fundamental level. What has changed to the wiring since the car rolled off the assembly line? Are you really discovering something new here that GM's engineers didn't know and they didn't catch during testing of the car? Do you think GM gave us these cars with a defogger and power seat that trip off early? Is there a left wing conspiracy to manufacture cars with undersized circuit protection? Why don't you just replace the part that broke with the same thing (which worked from the factory and will work now) and move on to the next thing that breaks?
Had you done a search and read all the other threads on this, you could have learned something and not gone through all the trouble to "calculate" yourself in to a problem.
Jeeze buddy, you either didn't understand what was said, didn't read everything in the post, or just want to stir the pot...1. Cutting open the breaker?? Did you see where I bought a brand new one and had the same results, the circuit cutting off early. I know breakers get weak I worked in Civil Engineering for 23 years...
2. 34 less than 35?? Duh... Yes, 34 amps IS less than 35, that's why the fuse does not blow and the system times out correctly. The 35 amp fuse handles the needed 34 amp current draw of the grid, works perfectly...
3. Worst advice? Install a higher amp breaker?? Pursue more logical and your conspiracy stuff??? Calculate myself into problem??? Well, you keep replacing that 30 amp breaker, and why not take it to GM for them to help spend your $. I never said to put a 35 amp breaker in there, I said a fuse. Your rambling on about conspiracies tells a lot about you... I calculated (with FACTS) the source of the problem with way too many people having problems with this circuit. I task you to check your grid with a VOM (if you know how to use one) and calculate the circuit current needed for proper operation. Or bring the grid resistance reading and source voltage at idle and at 2000rpm to the forum and I'll calculate your current draw for that grid. Then when you come back with the facts, you can see why the breaker keeps tripping on a whole lot of peoples cars since right out of the dealership lot.
4. Had I searched... I searched and searched when I first encountered the problem, nothing on my car has changed since then the system has worked many times (sometimes two and three times activated right after the other). I do my research, how about you doing yours and try to comprehend my OP and follow-ups I posted
I don't have a problem, seems a couple of the members have one. If you want to criticize then go somewhere else. If you want help with your recurring early defroster timeout, try this solution. Just be sure to not modify or add anything else to the circuit. Peace out all!
01-20-2014, 12:05 PM
#11
01-20-2014, 12:38 PM
#12
I had this problem and it was fixed just by swapping out the breaker with a 30-amp fuse. Worked perfectly ever since. Replacing the 30-amp breaker with a fuse of the same amperage has always been the tried and tested solution to the defogger issue.
Just because something has worked for you doesn't mean it will work for everyone else.
Just because something has worked for you doesn't mean it will work for everyone else.
01-21-2014, 07:06 AM
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I had this problem and it was fixed just by swapping out the breaker with a 30-amp fuse. Worked perfectly ever since. Replacing the 30-amp breaker with a fuse of the same amperage has always been the tried and tested solution to the defogger issue.
Just because something has worked for you doesn't mean it will work for everyone else.
Just because something has worked for you doesn't mean it will work for everyone else.
Tried that, fuse blew after a few seconds (like I figured).
01-21-2014, 07:10 AM
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Sorry, I was wrong - an ATC/ATO fuse will hold a 10% overcurrent for 100 hours minimum (not just four hours). Here is a link to the specs including the time-current limits: http://www.optifuse.com/fusesautoblade_reg.php. There is a similar document from Littelfuse but it shows the limits in a graph which is more difficult to read because the curve is logarithmic and the page is small, so I figured the OptiFuse chart would be a better choice.
And what does your chart say about a 16% overcurrent on a littlefuse? OK if you don't like the fix don't use it. I don't give a rats a$$ if you care not to use it. For those who would like to spend less than a buck and have 9 spares (10 ea for .99 cents with free shipping on flea-bay) go use it.
01-21-2014, 07:16 AM
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Hey if you don't like the fix I use, then don't use it. <Inappropriate commentary removed> Bad breaker, other problem with my car. NO... I do have a problem with people who hide behind their keyboard and criticize a well thought out and tested fix for a problem way too many owners have. Keep your comments off the thread, they are not appreciated. <Inappropriate commentary removed><Inappropriate commentary removed>
Last edited by wssix99; 01-21-2014 at 08:51 AM.
01-21-2014, 07:58 AM
#17
I think you're missing our point... for the vast majority of members who have experienced the early cutout problem, simply replacing the 30-amp circuit breaker with a 30-amp fuse has solved the problem. That's because the common problem they were experiencing was the aging of the circuit breaker making it trip too soon.
Your problem seems to different in that you have too much current draw from the defogger for any 30-amp circuit protection whether fuse or circuit breaker. Your solution for that unique problem may be workable for you but is not good advice for someone who has the more common issue of just a worn out circuit breaker.
But anyway, since you seem to think that you should be able to post whatever you want without anyone posting opposing viewpoints and then start childish tantrums when somebody does disagree - this thread is being locked whether you like it or not.
Your problem seems to different in that you have too much current draw from the defogger for any 30-amp circuit protection whether fuse or circuit breaker. Your solution for that unique problem may be workable for you but is not good advice for someone who has the more common issue of just a worn out circuit breaker.
But anyway, since you seem to think that you should be able to post whatever you want without anyone posting opposing viewpoints and then start childish tantrums when somebody does disagree - this thread is being locked whether you like it or not.