Rear Window Defogger

[formzy]

I have a'90 Lesabre and when depressed the window defogger switch lights up and only stays on for 2-4 minutes. According to the electrical shop manual for this car the first cycle of the ignition switch should stay on for 10 minutes and then when depressed again 5 minutes. The manual says to replace the control (switch) if the time is more or less than this.

I went to my local junk yard and retreived several of these switches very reasonably. I tried all of them and had the same results. A couple didn't even light up but the rest worked the same as the original. My question is could the relay be the culprit here or could all of these old switches be bad.(odds against but possible). Does anyone think the relay is cutting off power too soon or does this relay just switch on and off and not affect the timing of the defroster. I know the switch has a timer internally that suppose to set these on times and then shut off.

Has anybody run across this problem before? I guess I'm just not sure the role the relay plays in this circuit. Maybe try another one? Hard to believe all (5) switches could be bad? Let me know what you think. Thanks

[HotZ28]

Here is a recent thread on the rear defogger. I know it is for an 97 PA, however, the defogger option is one thing that has not changed much in the past twenty years!
BTW, did the switch look like it included a timer circuit?

[rustbucket]

I had the same trouble on my 87. opened up the whole thing, found no problem. Then I checked the fuse, Swapped it with another one, and defroster worked correctly.. So I opened up the silver can fuse, It was a thermal type one (heat causes contacts to open) and looked like it had been getting too hot. I assumed at the time that that was the way they did the delay. Apparently the fuse was getting hot sooner than normal.

[HotZ28]

Originally Posted by rustbucket

Then I checked the fuse, Swapped it with another one, and defroster worked correctly.. So I opened up the silver can fuse, It was a thermal type one (heat causes contacts to open) and looked like it had been getting too hot. I assumed at the time that that was the way they did the delay. Apparently the fuse was getting hot sooner than normal.

The item in the "silver can" is called a circuit breaker. BTW, good idea to check that too!

[Bassasasin]

Yah.. Thermal Circuit Breaker crosses my mind.

Perhaps it has a loose connection near the breaker.. If it shows its getting hot that is the way it works... Perhaps its getting hot unnecessarily..

Didnt know thats how it works..
Thanks Hotz28.

Good Luck formzy..