02LS1Z28BC

iTrader: (4)

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 +/-, instead of the approximate 10 minutes +/- time posted in the manual. Thinking the CB was bad (least expensive option), I replaced it with a new one (I now have two unused 'spares' to this day) Thinking the panel assembly was defective I replaced it (same result, almost to the second 5 minutes CB tripped). I then took resistance readings & voltage readings under various rpm's at the REAR WINDOW grid terminals, and found the 30 amp delay action breaker was under-rated (for this circuit) by almost 4 amps (for my B4C circuit of a drivers seat and the defogger grid). IF YOUR GRID (ON THE WINDOW) HAS TOO LITTLE A RESISTANCE VALUE FOR THE VOLTAGE APPLIED THEN YOU HAVE SOME WORK TO DO TO FIND OUT WHY.

I have the service manual set and verified the wiring size all the way to the defroster grid. It was ample in size to handle the almost 34 amps needed for the power supplied to my grid circuit (Make sure there are NO ADDITIONAL ELECTRICAL DEVICES ADDED TO THAT CIRCUIT PATH IN ITS ENTIRETY). If you do the PROPER work, verify the wiring is adequate and OEM, measure all values at least twice with a good VOM (I use a Fluke), DO THE MATH (using ohm's law for DC circuits), make sure you check all the values are plugged in the correct places in the equation, on the grid with the actual voltages/resistance YOU measured on YOUR car, and you may find the REASON the CB is tripping. and you may also find a solution for your individual situation.

My solution, 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! This has been working for me since late 2009. The fuse doesn't blow/get any hotter than ambient IP temperatures, doesn't turn my car into a 'charred mess', or any other detrimental presentation. I do not suggest anyone else use this method, but if you do you MUST do every step to insure each link in the chain is ample to handle at the most a 16.666667% increase in the RATED circuit rating (install of 35 amp fuse where slightly less than 34 amps are drawn for MY grid) vs the 30 amp breaker (designed) rating (in the IP fuse block location in the B4C) . There are only 2 high current electrical devices on my B4C that uses that circuit, the rear defogger and the drivers seat. I do not believe I would be moving the drivers seat while defogging the rear window (and I believe the engineers who designed the car would not have thought that either for ANY length of time beyond a few seconds). So, IF your defogger grid measured too low of an ohm reading with a low voltage (system at idle) applied, MAYBE this fix can work for you. Remember, NO ADDED MODS in that circuit, NO broken/frayed wiring, and your readings for the DEFOGGER GRID VOLTAGE at VARIOUS RPM's (especially at or near idle), must be checked/rechecked.

As usual, if this is way beyond your individual capability I suggest you not do what worked for me. I offer this post as my solution to an inexpensive and safe (for me) solution to replacing the rear defogger window in my 14 year old car (not knowing what the resistance value is/was/would be) with any 'replacement' rear window . This was after replacing the 30 amp breaker (again, I now have two spares), another HVAC control (with internal defogger switch/relay(?)/timing circuit) with indistinguishable differences and no success (again, also two control heads, one in the car and one in a box).

Taa Taa!

PS: 100

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WhiteBird00

iTrader: (4)

Did you try replacing the circuit breaker with a 30 amp fuse? Most members here have found that due to the built-in overload capacity of standard fuses, the defroster will run its full 10 minutes without having to use a higher rated fuse. This is because UL (and CSA in Canada) standards specify that a fuse can carry 135% of its rated current for up to 60 minutes. That would be 40.5 amps for a fuse nominally rated at 30 amps - more than enough to handle 34 amps for 10 minutes.

You did a great job of investigating and calculating and I applaud you for your excellent post. However, the tolerance factor of your 35A fuse means that you could potentially allow over 47 amps to run through the circuit for up to an hour before the fuse would blow. I recommend installing a 30A fuse instead.

wssix99

iTrader: (5)

+1

This is my favorite thread on this topic: (there are many...) https://ls1tech.com/forums/stereo-el...er-switch.html

Once upon a time, I looked up the delay specs on the breakers and fuses and found that the breakers had a longer delay. I'm not sure what is on the shelf these days, but the breakers do have the added downside of the deterioration issue. (Cut open your old breaker for a nice show.)

I just replace the breakers when they wear out, but I don't think I've ever seen anyone having a problem after moving from the breaker to the fuse.

02LS1Z28BC

iTrader: (4)

Once upon a time I mentioned the fuse (30 amp) blew right away. Although I don't remember if I tried others, I would not have given up on one or two fuses (30 amp) as I have a bunch of them always available.


As the post indicated, replacements (breaker and control panel) failed to resolve the higher current drawn by the grid (AS TESTED).


This post is informational only, my solution worked for me. Thanks for your comments.

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