When I turn the rear defroster on on my '87 TA it works, but it cuts off _way_ too fast, like something on the order of after a minute or 2. The whole grid works, it seems to turn on and off correctly, just the relay cuts out really fast. I also tried pulling the relay from my '87 parts car and swapping it and it does the same thing.

Any idea what might be causing it? alternatively, is there any way to make the thing stay on much longer (if I remember right it's supposed to stay on for 11 min, something like 11-15 min would be nice)

 

anyone?

 

My 84 does the same as yours!
Since you swapped the relay I know thats not the cure to the problem.

I guess I will chalk it up to the cars old age...................

 

I dont think the relay has anything to do with the timing of the heat. Its either a separate unit...like in the convenience center, or in the switch itself. PRETTY sure its controlled within the switch but dont quote me. I know mine on my 86 and on my 87 stayed on longer than a couple minutes. Not sure if it was quite 11, but a good deal more than 2.

Check the wiring diagram, or google/search around here. Gotta be some info on it.

J.

 

I would think it's the Timer Relay,what else could it be,maybe the Defogger Switch itself ??
The Defogger Relay is located on the R/H side of the I/P near the ECM. P/N 10017711.

Hope this helps you out.
It's supposed to run for 10 mins.if you hit it off and on 2 times it will run for 5 mins.

 

Right, this thing:


I have 2 of them sitting around, I tried both, they both turn off at between 35 and 37 seconds. Unless they tend to fail the same way (not sure what that failure would be, it looks like it's just a simple solid state timer circuit and a relay inside), I'm not sure that replacing it with a 3rd one will make any difference. I don't know what else to check... I'm wondering if i might have intermittent power or ground to it causing it to shut off momentarily like when I hit a bump, but I don't have a really good idea how to check that.

 

Just a thought...................

The weather has turned real cold and snowy here in NY.
My car was parked outside and snow covered. I started it up and let it run with
the rear defrost on. The rear defog stayed on for a good 10 minutes and melted
the snow off the back window!

I wonder if the outdoor temp. or window temp has something to do with the
extended defrost time????

 

I would seriously check the 35 amp circuit breaker and defogger switch,unless you have 2 bad relays that your using,

 

Behind R/H Side of "IP", that's up under the dash on the passenger side?

 

That would be the R/H side!!!!
Oh,your passenger seat is our drivers side!!!!!!!!didn't realize that until your last post

 

I just wanted to make sure. I replaced some really corroded wires in the back and it still stays on for only about 1-2 min initially, alot less if I push it again. Kind of a bummer really. I was hoping that the corroded wires were creating a resistance that was popping the relay. Guess not. hehe Now I have to order one, wait 7-10 business days for it to ship to the UK and pay a rediculous amount for international shipping. /sigh haha Ah the life of not living in the US with an American car. hehehe

 

your picture is fuzzy so I can't tell if it says 35 or 30A, but interestingly, both my '87's had 2 30A breakers in them. I swapped both (didn't bother checking which one was actually the defroster breaker, quicker to just swap both) from my formula (where the defroster was working correctly) into my TA... I'll try it tonight when I go to the gym. I suppose that the breaker might just be intermittent...

 

Sorry about the fuzzies,it would be a 35 amp circuit breaker.

They do reset.

 

Window defogger, Relay
Window defogger, Switch
Pontiac, w/o Spl Ed Trans Am
List Price : $31.09 switch
Your Price : $24.87
All Models
List Price : $51.93 relay
Your Price : $41.54
WOW!!!these are expensive.

 

didn't make any difference...

I'm sure that the switch works, that the breaker is OK, I'm fairly certine that the grounds/contacts are OK... I have 2 of the timers doing _exactly_ the same thing... any other ideas?

 

Try swapping out the switch. Yes, it may work, but there may be an issue with the OFF button that's turning the defogger off early.

The timer is supposed to be on for 10 minutes the first time the ON switch is pressed and 5 every time after that until the ignition is turned off.

 

I've ordered the relay. I can hear it clicking, more than once when i turn it on. One time it actually buzzed at me like it was continuously flipping states on/off. We'll see if that fixes it. I'll keep you guys posted. Should be getting the relay in the mail in the next week or so.

 

After swapping the breakers I timed it and got just under 3 min the first time, and between 30 and 40s after that. I'd be very surprised if it was that consistent if it was a problem with the switch. Off the top of my head i don't remember if the formula has the same switch, but if it does I'll try swapping it over the weekend, but I sincerely doubt that it's the switch. So far everything that I've swapped from car to car has made no difference in how it performs (yea, I might be posting a slight change in numbers, but that's really just a matter of playing with it more and getting a better impression of what it was doing)

 

Not supposed to stay on for 3 minutes,nor 30-40s minutes,it's got to be the timer relay because it's not consistent with the way the relay works.

 

I wonder if the timer switch isn't voltage driven, and you've got a draw on it on the line somewhere. Either a bad ground or broken/crimped/corroded wire that's drawing more power causing the timer to mess up.

 

Where did you get the relay? My parts guy said they were no longer available.

 

GM parts direct I Think it was. I just put the part number in google and found it that way.

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Edit

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I just learned they refunded my payment through paypal....crap.

Well, time to start looking again.


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edit
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I've found one used one on Ebay.

 

You could try your local GM dealer for the part and if they don't have one, they will supply you with a list of other dealers that may have them in stock.

 

I'm going with the one on Ebay, it's local of all things here in England. Surprised the hell out of me! haha If it works, cool, if not, I'm out $10.00.

 

Has anyone tried measuring the voltage across the circuit? I always thought that as the grid heated up it passed either more or less voltage, causing the relay to open when it reached a particular potential. For example 12 volts applied to the circuit would let a small amount of amps through if the resistance was high. As the grid heated up the material would become more conductive and thus the resistance would drop. This would increase the amount of voltage that was allowed back to the relay. Probably not right but might be worth investigating.

 

Except that resistance INCREASES with heat...

 

Well resistance on some things increase with heat. On other devices resistance decreases (like in a coolant sensor for example, 450 ohms at 70 deg. 0 ohms at 285 deg). I haven't had a chance to check how the defroster circuit reacts to heat yet, but the idea was that perhaps the relay was sensitive to voltage or current changes. Just an if the timed relay idea wasn't resolving.

 

thats why if you watch breakout kings or whatever it is and they defuse the bomb with the freyon, you can say thats incorrect. lol