[dusteravenue]

I have a weird problem with my rear window defroster. It simply won't melt even a snowflake off the window.

BUT,

It has power on the lines on the glass, the switch works, the lift struts conduct the electricity. I can probe any line on the glass at any place and get battery voltage.

By troubleshooting techniques it should work... but it doesn't. It doesn't make sense how there can be power to the grid lines on the glass but not warm up.

What is the theory of operation for the rear window defrost? Is there more to it than just power to the lines. None of the line are broken or missing. I used a volt/ohm meter and checked every line.

I am stumped.

 

[oldeerslayer]

I'd ask the guys at the Blazer forum. This would be a more common issue there.

 

[MyWorkInProgress]

You get both power and ground through the strut tabs, if you’re getting power with your probe and no heat that means you have a bad ground. Should be easy enough to track down and if not get out the soldering iron and make your own. Look up @deathphoenix99 he has a bunch of wiring diagrams posted to get you sorted out. When mine went out I just had to clean up the strut connection to get ground. Good luck.

 

[dusteravenue]

You get both power and ground through the strut tabs, if you’re getting power with your probe and no heat that means you have a bad ground. Should be easy enough to track down and if not get out the soldering iron and make your own. Look up @deathphoenix99 he has a bunch of wiring diagrams posted to get you sorted out. When mine went out I just had to clean up the strut connection to get ground. Good luck.

I didn't think of that. I was so focused on 14.2V at the grid, with the probe on a interior trim screw for ground. It never even donned on me that there needs to be a ground on the somewhere on the back glass.

 

[dusteravenue]

I think I might have solved the issue. I haven't left the Jimmy outside to get the back window snowy/frosty to be certain yet though.

It was definitely a ground issue. My electrical troubleshooting technique was flawed. I was probing power/grounds with all the wires hooked up. Of course I would get 14.2v when I touched the grid/bus bar and a body ground. It wasn't until I took the body ground lead off the passenger strut that I found out that it wasn't grounding/creating the circuit.

The issue was the lift struts from amazon. The passenger one wasn't creating the circuit. I twisted it and moved the tabs a bit and it now reads that it conducts electricity.

The final test will be when the window is frosty, but I hope all will be well.

 

[Walleye Hunter]

I think I might have solved the issue. I haven't left the Jimmy outside to get the back window snowy/frosty to be certain yet though.

It was definitely a ground issue. My electrical troubleshooting technique was flawed. I was probing power/grounds with all the wires hooked up. Of course I would get 14.2v when I touched the grid/bus bar and a body ground. It wasn't until I took the body ground lead off the passenger strut that I found out that it wasn't grounding/creating the circuit.

The issue was the lift struts from amazon. The passenger one wasn't creating the circuit. I twisted it and moved the tabs a bit and it now reads that it conducts electricity.

The final test will be when the window is frosty, but I hope all will be well.

I'm not going to discount your claim about amazoo, I don't like them and am wary of what comes from them and fleabay. Though I do buy stuff off of fleabay, both are known to offer counterfeit merchandise and what they are willing to counterfeit is unbelievable. All that being said, I got a new set of struts from Parts Geek, that were touted as genuine AC Delco and had the same problem that you did. I had to manipulate the tab on one of the struts to get it to pass current. I wonder how long it will be until I have to do that again.

 

[1985BlazerS10]

I have also seen lift struts that are supposed to conduct current, but do not. I think it's a legacy product issue where the manufacturers and distributors just don't care because we're too small a market.

 

[dusteravenue]

I guess success. The only real test I got was turning the defroster on for a few minutes before I got home. The Jimmy sat outside for 10 hours in -30 and I put it into a 62 degree garage. It instantly fogged up but the rear window was clearing up fast and I could see where the lines were heating.

 

[Hamilton Felix]

Maybe it’s because I’m retired from the electrical trade, but that seems weird to run the defroster circuit through both lift struts. Mine are presently screwed up. I’m thinking I may have some leftover type SIS hinge wire from my working days, maybe just create a dedicated circuit independent of the struts.