Rear Defroster not getting hot

mack_psu

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I just purchased a used 2016 Civic EX-T in late January 2019.

Over winter months I noticed (similar to other threads on this forum) that the rear defroster in this car is not very good.

This week, I borrowed a thermal camera to take some images. I started the engine, and pushed the button for the "side mirrors and rear defroster". The side mirrors get red in the thermal image and are warm to the touch. The rear defroster stays blue on the thermal camera image even after a couple minutes. I can touch the grid lines and they are cold. So I started troubleshooting...

I checked the multi-block fuse (PN 38233-TBA-A01) located inside the engine fuse/relay box. the positions all looked good. I used a multi-meter to check for good continuity from the metal screw post to the bottom metal posts. All were continuous (shorted) so that tells me the fuse is good.

With the engine off, I checked the relay which is called out on parts diagram under control unit (engine room) as item #2 (PN 39792-SDA-A01). it is a four post relay. i checked for resistance between two of the terminals and that looked good. i did not try to actuate the relay by applying 12V to the relay.

Next I used a multi-meter to check the grid lines. they look good and do not have breaks. I checked resistance between a line at the top of the window and a line as low as i good go. I wrapped a piece of aluminum foil over the probes so I had more surface area to touch the wires. the multi-meter read as a short. I think that means that there are no breaks in the window grid.

I turned on the engine again and checked voltage on the grid lines. my ground lead was on the metal rear door strike plate. with the rear defroster OFF, I read zero volts. With the defroster ON, I read 12-14V.

This tells me that the grid lines are getting voltage, but no high current is going across the grid lines.

can anyone help with next step troubleshooting? Are there other relays or fuses in other locations that I need to check?
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ken88

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Unfortunately I think it's normal; it's one of the few complaints I've had with my Civic - the rear defroster just isn't that good.
Last summer I ended up working midnight shift and I'd use it on the drive home to clear the dew off.
I have about a 15-minute commute and I'd already be halfway home before the rear window was cleared.
 
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mack_psu

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Have you ever tested your defroster or checked the voltage on one of the grid lines when it is on? If you have a multimeter can you please measure voltage (when defroster is off and on) touching one probe to door strike plate and other probe to one of the window grid lines.
 

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This car has the slowest defogging/defrosing rear defroster of any car I've owned.
 
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mack_psu

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Thanks for the replies

think I figured out the issue. There is no solid connection between ground and window grid.

I removed the passenger side c-pillar. I checked the ground cable that attaches to the defroster grid. The cable looks good from metal post to grid connector. The grid is attached and seems to be well bonded to the window but the clip is not electrically shorted to the window grid. It looks like the previous owner already had an issue with this and at least one repair was attempted. Looks like the area around the defroster clip on the window was sanded lightly

Any suggestions for a conductive epoxy to make a better electrical connection between defroster clip and window grid?

Advance auto sells a window grid epoxy that looks like it has copper properties. It’s called permatex defogger repair kit.

Also found a couple two part conductive epoxies. One is MG Chemicals 8331 Silver Epoxy Adhesive. About $50. The other is frost fighter bonding repair kit around the same price. Even though the 2-part epoxies are more expensive these seems like a better option.

Any recommendations?
 


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My first impression was that someone tried one of those repair kits (hence the sandpaper scratches); but didn't follow directions carefully.

If it were me; I'd shop around on Amazon and read the reviews (and comments). Find a shady spot on a cool day when you have time to not be rushed and try the repair again. It looks like the prep and mixing the adhesive properly are the tricky parts.

Good luck with it and post the results when you pick an option.
 

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Thanks for the replies

think I figured out the issue. There is no solid connection between ground and window grid.

I removed the passenger side c-pillar. I checked the ground cable that attaches to the defroster grid. The cable looks good from metal post to grid connector. The grid is attached and seems to be well bonded to the window but the clip is not electrically shorted to the window grid. It looks like the previous owner already had an issue with this and at least one repair was attempted. Looks like the area around the defroster clip on the window was sanded lightly

Any suggestions for a conductive epoxy to make a better electrical connection between defroster clip and window grid?

Advance auto sells a window grid epoxy that looks like it has copper properties. It’s called permatex defogger repair kit.

Also found a couple two part conductive epoxies. One is MG Chemicals 8331 Silver Epoxy Adhesive. About $50. The other is frost fighter bonding repair kit around the same price. Even though the 2-part epoxies are more expensive these seems like a better option.

Any recommendations?
Just to clarify, when you say "the clip is not electrically shorted to the window grid", do you mean the the connector on the glass is not making contact with the grid on the glass? Is there an actual air gap between the two?
 
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mack_psu

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The defroster tab/clip is glued/bonded to the window. There does not appear to be an air gap.

When I use a multimeter on continuity setting, the meter beeps when one probe is on one grid line and another is on a different grid line. It also beeps from large top to bottom strip to any window grid line

The meter does NOT beep when one probe is on the defroster tab and the other probe is on the large strip from top to bottom of the grid or any window grid line.

It looks like the tab may have fallen off and someone tried to reattach in a slightly different position. My guess is the person used more bonding agent than metallic conductive agent

The reviews online state that users have used the MG chemical 8331 exactly for the defroster tab because it is a silver conductive epoxy.

My hope is to use the silver epoxy around the large grid strip and the defroster tab so that the ground connection is more reliable.

See uploaded picture. the defroster tab is glued to the window. the ground wire is disconnected.

Honda Civic 10th gen Rear Defroster not getting hot 514641A9-B503-4ADC-9EBB-F297B479F430


Honda Civic 10th gen Rear Defroster not getting hot C1ACAE9F-3156-4CDE-8D0D-154CE324C43B
 

BriteBlue

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Thanks for the information. Makes me wonder if someone just tried to use a regular glue to re-attach the clip.
 

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Yikes. That doesn't look very carefully done.

I wonder, just for a test, if you could just fold some aluminum foil (shiny side out) into a small wedge and put it between the bottom of the clip and top of the element in the space where it doesn't normally touch.
 


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mack_psu

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Well this has been an adventure. I successfully used the mg chemical 8331 silver epoxy. I connected the ground wire to the tab and the defroster works. I used the thermal camera to find a few broken lines also. I fixed the lines as well using the same silver epoxy and used painters tape as a border. I used a q-tip to spread the epoxy on the window grid lines.

However I used a toothpick to spread the epoxy. I should have used a q-tip for the tab also. When I used the toothpick I may have spread too much epoxy because now when I turn on the defroster within 2-3 minutes there is a little smoke coming from the area of the tab. I looked on my thermal camera and the tab is white hot above 200-250 degrees F. This is probably really dangerous. I don’t know if this is it for the rear window defroster.

Anybody have any ideas? I have to determine a way to dissipate or spread out the heat around the tab. All of the heat is dissipating right at the tab where the silver epoxy is located.

The only thing I was thinking about was using a q-tip to spread a line of the silver epoxy from top to bottom. This may help spread out some heat. I’m looking for feedback or some ideas before I throw in the towel.
 

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Yeah. That doesn't sound good.

Just something that occurred to me just now... Check the fuse and make sure that the previous owner didn't switch a higher value fuse in there. It may not be the cause of anything. But you definitely want to keep the wiring safe.
 

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It seems there is a high resistance connection which is why it gets hot. That would mean not a good connection.

Was the tab actually off of the glass & you epoxied it back on? Or did you apply epoxy around the already attached tab where it meets the grid?
 
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mack_psu

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The fuse is the correct fuse

The tab was not off the glass. I applied epoxy around the tab where it meets the grid
 
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mack_psu

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I believe I have determined that I applied too much of the silver two-part epoxy. I purchased a new defroster tab and held it in place and the point where the defroster tab touches the window grid only gets to between 100F—150F.

How bad would it be to leave the tab with too much epoxy in place and glue a new defroster tab in front of it? Then I would use the existing ground wire to connect to the new defroster tab. I don’t want to try to pry the existing tab off because I do not want to permanently break the grid or the window glass

I think my remaining options are use a small amount of silver epoxy for the new defroster tab or just purchase a a new rear window. What do you think?
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