Rear window defoger not working

[81 Checkmate]

2003 Chevy Tahoe

It worked last year and now we are starting to have cold dew mornings. Well it's not working

Push the button and light comes on at the dash...... Unplug wire and Check voltage on the plug going to tang on the pasenger side 12.7 volts. Plug it in and check tang again 0 to .5 volts. Clean tang and plug back in and have 12.7 volts on tang. Good power coming too window.

Go to other side (Driver) unplug and check tang 12.7/13.5 volts..... Good power across the window...Then as soon as i plug (Driver side) back up and check tang back to 0 to .5 volts. Cleaned tang and plug and same results.

Cant check to see if it works till it fogs up again.

Never been an electrical guru. :facepalm: Am i missing something?

 

[MTboatguy]

Re: Rear window defoger not working

You have a broken grid line on the back window, they sell copper laced kits to fix this problem at most auto parts stores, they cost around $10.

All it takes is a hair thin scratch across one of the grids to make it not work

 

[fat fanny]

Re: Rear window defoger not working

Check if you have continuity across the tabs on the elliment could be a short in the power plug and or connector? Some window replacement shop repair the eliments. Good luck post back results!

 

[81 Checkmate]

Re: Rear window defoger not working

Rechecked the grid. Driver side plug unpluged from tang....Pasenger side plug on tang.

Checked voltage at tang on driver side = 12 volts coming in the grid
Checked each grid line at each end and showing = 12 volts going out the grid

Plug the driver side plug back to tang and reading .05 volts

Im thinking the grid is ok. Am i right to assume this from the testing ive done?

Why is it droping when i put the plug back on?

 

[fat fanny]

Re: Rear window defoger not working

You could have ashort to ground on the driver side plug trace it back to it's source most likely the switch and or fuse block. At the it's fuse check continuity from the fuse terminal to the end of the plug wiggle the lead while performing this test and check all crimps and or connection points and check across the grid end to end for continuity. Another good test is use a simple test light ground it and plug it into the driver side plug and turn the switch on if it lights it's ok if not theres the start of your problem. try it post back.

 

[81 Checkmate]

Re: Rear window defoger not working

Fanny i think your on to something.

Been reading how it works...... the two wide bands on each side of the window should have 12 volts going to them at all times...then they heat the element inbetween them on the grid.

In gona leave the driver plug off and try it in the morning and see if half is working.... Lower 60s tonight dont think its gona happen :facepalm:

Will let ya know when i find the problem....

Thanks for the advise.....iboats people!

 

[rockyrude]

Re: Rear window defoger not working

Not sure how they do it now, there used to be a relay to handle the current the grid requires. This is also a timed circuit, you may have noticed that after a certain amount of time, it turns itself off. Check to see there is a relay, the contacts can burn and go high resistance dropping the voltage to the grid.

 

[CharlieB]

Re: Rear window defoger not working

One side of the circuit is 12V, the other side has to Ground.

Unplug both sides, test to see which side is 12V, the other side HAS TO ground.

From what you have posted it appears the pass side is 12V and the Drivers side is the Ground.

With the circuit plugged in and turned On, you should measure 12V on the power side and little or no volts on the ground side.

You may have already fixed the poor connection just by unplugging and reconnecting the wires.

 

[81 Checkmate]

Re: Rear window defoger not working

Charlie is guess im reading the info wrong on how it works.

What you are saying is what i have......12 volts on one side and .05 volts on other side. The dash switch lights up and 10 min later the light goes out. So i think the relay and switch are good.

Tried the unplug thing this morning and it didn't get cold enough last night to see if only half works......I will plug it all back up and wait and see what happens.

Thanks for the info!

 

[bruceb58]

Re: Rear window defoger not working

The dash switch lights up and 10 min later the light goes out. So i think the relay and switch are good.

No guarantee the relay is good.

 

[81 Checkmate]

Re: Rear window defoger not working

Bruce are the relay and switch one unit in the dash? Or are they seperate

 

[bruceb58]

Re: Rear window defoger not working

seperate

They are less than $5

Not that its your problem. I hear that the problem is usually the connection at the window.

 

[81 Checkmate]

Re: Rear window defoger not working

Thanks! Ill pop off the dash panel and have a look.

$5 Bucks thats a godsend compaired to the BOAT parts - Dealer item or do you think Napa will have them?

 

[bruceb58]

Re: Rear window defoger not working

rockauto.com

 

[Pascal]

Re: Rear window defoger not working

try page 15 on this link........

http://assets.fluke.com/appnotes/automotive/beatbook.pdf

It is a good save for other electrical problems as well.......