When you turn it on it does work, but it turns itself off after probably a minute, not enough to actually do anything.

Anyone know how to get it to stay on longer?

 

does it not defrost AT ALL? or does it barely defrost and then turn off. if it doesnt turn on at all then check the wires where your rear hatch shocks are, its pretty common for those wires to come unplugged. if it comes on but does nothing then mayb wipe your window down because you may have too much moisture and the defroster cant do the work so it shuts off. both things happened to me countless times.

 

Like I said, it does work, if I punch it on like a dozen times it will defrost the window, it just won’t stay on a reasonable period of time.

From what I understand it’s supposed to turn on for 10 minutes the first time and 5 every time after that. I’m lucky to get a minute any time…

 

if your talking about your 83, there are 2 things you want to look at first which may be your problem.
the first is the circuit breaker in the fuse box. its a 35 amp breaker & may not be able to carry the load it needs to & shuts off too soon. i had the same problem on my monte carlo a few years back & the breaker was it. i would recommend to go a head & replace it, they are pretty cheap & its a good possibility its your problem. if you have power windows, they should also have a 35 amp breaker & you can swap them out & see what happens.
if you do buy a new breaker, be sure you get a 35 amp, a 30 is too small & won't carry the load, a 40 is too big & can damage your wiring if there is a short.
the other thing is the timer relay, i would only think about replacing it after you have replaced the breaker with a known good one.

 

Where can I find a 35 amp circuit breaker from? I have look all over but can not find one. Do yoiu have any suggestions?

 

most any parts house should be able to order one if they don't have it in stock. if nothing else, the dealer should have them.

 

I don’t know if it makes a difference, but it’s my ‘87TA… I’ll poke around some tomorrow… thanks

 

they both use the same setup.

 

Well, I swapped the breakers (both, didn’t bother looking up which was which) with the ones in my formula (the formula is an ’87 also)…

No change.

Swapped the timer/relay assembly with the one in the formula… no change again.

FWIW, the factory service manual first has you check that it turns on, time how long it stays on and if it comes on and doesn’t do the 10/5 minutes thing then “replace the timer/relay.” So I’m at the end of their diagnostic.

Any other ideas?

 

 

Parts car with working parts 4’ away trumps test light with burnt out bulb 50’ away in the garage or DVM, through 2 doors, about 20 carpeted steps (have to do something with snowy/wet shoed) and 50’ away.

Even if they were equal distances, at that point finding an exposed wire on the load side that I can easily get to would be enough more work that swapping the other breakers in 10 seconds would still win.

Like I said, swapped it for a known good one from the parts car and it still does the same thing.

Looks like a simple 555 timer circuit (can’t tell for sure since the board is mounted on stand offs above the relay face down so you can’t read the labels on any of the components without disordering the board from the standoffs). But that’s sort of irrelevant. If this was a daily driver that I wanted exactly 17minutes worth of defrost time from then I would bother, or at least look at it some more, but this is a project, semi race car that sees street time, I just want the damned thing to work. Since the easy diagnostics don’t seem to show what’s wrong, and I doubt that the car will see more then a few minutes driving in bad weather at a time, I’d be fine with figuring out how to just turn the defroster on and have it stay on till I shut it off or turn the ignition off since that would be just as functional in this situation.