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Discussion Starter · #1 ·
So your rear defroster don't work. This write up will help you diagnose the problem, and fix it.

Note to all. The pictures were taking from an online manual for a 1988 Honda CRX. The information is from a 91 Honda CRX Si. Some things are different but mostly the same.

Lets start out with the easy stuff. First check you fuses. There are two that power the rear defogger. One is in the fuse box under the dash(10A) and one is in the main fuse box under the hood(20A). If blown, replace.

Now for the more difficult stuff. Tools that are needed are a multi-meter, some jumper wires and a wiring diagram (included in this write up). Its also a good Idea to have extra fuses, just in case.

Switch Testing
The easiest way to see if you switch is working is to see if the light comes on when pressed. But, the switch light could just be old (it is 15+ years old) and blown out. To test, remove cluster cover for best access to the wires and switch. First, check to see if power is going to the switch. Take the multi-meter and set it to volts. Find a good ground and place the black lead on the ground. Take the red lead, and press it into the hole on the back of the connector where the black and yellow wire goes in. It should read a voltage. If not, check fuse again to make sure you did not blow it. If that's not the problem, you have a open some where on that wire. Trace the wire and replace bad section. Don't quote me on this part but Switches from 88 and 89 are different from the 90 and 91 switches in that the 88 and 89 don't have a time dial (not expert word). The 90 and 91 switches have a dial that turns and after about 15 minutes, turns the switch off. The 88 and 89 don't seem to have this. Once again, don't quote me on that part. To test an 88 and 89 switch, check continuity between pins A, B, and C (when switch is on) and then check D and E. If no continuity, replace switch.

Testing the Relay
This is, for the most part simple. Remove the relay from the fuse box.
Looking at the relay you'll see four pins. A, B, C, D Some are labeled while others are not. A and B is the switch side of the relay where C and D is your control side. Place jumper wires on C and D and test for continuity on the A B side. If there's continuity when there's power going through the control side on the switch side and there isn't when you disconnect the power, your relay is good. If not, replace with new one.
Next, check you see if you have power going to the relay. Once again, find a good ground and place the black lead of the multi-meter on it. Then, take the red lead and place it in to where the A pin would be(yellow and green wire). You should read close to 12 volts.

Rear Window Defogger
First things first, check to see if power is going to the elements. (Note: The ignition switch and defogger switch need to be on for these step.) Find a good ground in the rear, placing the black lead of the multi-meter on it, and place the red lead on the drivers side (positive side) connector. You should have close to 12 volts. If not, trace wire back to find open and replace bad section. Next, check the ground side continuity. Place one side of the leads of the meter on a body ground and the other lead on the passenger side (negative side) of the elements. If no continuity, trace the negative wire and replace bad section. For testing the defogger wires, us the multi-meter to check voltage from the middle of the wire to the negative side connector. The meter should read 6 volts. Check the rest of the defogger wires the same way. If there's no voltage, that wire is bad on the power side. If there's 12 volts, that wire is bad on the negative side. To fix a bad wire, First clean off around the bad area, and then masking area the area. Use a silver conductive paint and apply one heavy coat that extends about 1/8 of an inch on either sides of the break. Check to make sure you fix works after allowing to dry with method above.

That should be everything with the rear defoggers. Hope this helps the many people out there with problems with there defogger.

Tom
 

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hey man good write-up, mine isn't working right at the moment, and I want it to, before it gets too cold out. I think i will print this off, and see what I can find out. Thanks.
 

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jfrolang said:
I actually tried that circuit writer pen and it didn't work so well. Maybe because I was trying to use it upside down. :lol:

Even oriented properly though, it was either not enough or too much at once.
Yea thats why I said it was OK. It still got the job I had on a pcb done but it was sloppy and cleanup because of the sloppyness was annoying. I wasn't pleased by that product. Yet it does work.
 

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Good write up Dodo...if I may add though..

When I test for inop defrosters.I start by checking the grid first.I find that most defrost problems are from a customer that has accidentally scratched the grid with something(i.e. umbrella,and other "hard" cargo).After I determine that the grid is ok I move on to the more uncommon stuff.

Also when checking for voltage or continuity it is very important to make sure your ground is good by trying to use a known good ground.To test for this I place my black lead on a "test" ground and use my red(positive) on something like the hot side of the cigar lighter.This tells me that my ground is good.
All in all good.I just wanted to clarify some things I saw that might have confused some.
Hope I helped ...
 

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As per the write up (which I found most excelant, thanks) the positive is on the Drivers side and the ohms(neg) is on passenger side.

However its seems that mine is backwards, positive on the passenger side and the neg on the driver side.

Is mine just wired backwards or am I missing something?

Bob
 

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I'm not all that familiar with that "pen" ,but I use a grid repair kit at my work that looks like this...grid repair kit Yeah I know boo JC whitney..lol,but you get the idea.

Anyhow I use plain jane scotch tape and paint away! GL...
 

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Discussion Starter · #13 ·
Im also not to up with the pen, but by looking at it, it seems flawed in that writing upside wouldnt work all to well. I have the paint type and was going to use it shortly after writing this, but yet still havent done it. The kit i have comes with a template at you tape to the window before "painting" on the product, but tape would work for larger areas where needed. I see your point though. Ollie, you seem to have used this more, does it come up when pulling the tape off?
 

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Dodo said:
Ollie, you seem to have used this more, does it come up when pulling the tape off?
Not for me.It comes off fine when I have had to do this in the past.GL on your repair..
 

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I know this tread has been on here foe while and , I have a problem with a couple of the wires on my defogger and did not know any repairs could even be done to the defogger, this is an excellent tread, and my wifes DD 91 hatch has a problem too, maybe the switch which I have replaced but not tested yet, anyway I know I'm late on this but thanks for such a great write up ,, very helpful..thanks......
 

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ollie said:
Dodo said:
Ollie, you seem to have used this more, does it come up when pulling the tape off?
Not for me.It comes off fine when I have had to do this in the past.GL on your repair..
When pulling it off dont just pull the tape any old way. Ive found the best way is very slowly pull away from the paint. Sorta looks like a 90 degree fold as you peel.
 
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