99 Cavalier rear defogger inoperative

[solcany]

Hi.

I have a 99 Cavalier rear defogger inoperative.

Ground side of window is good.
12Vdc side has no voltage
30A fuse for this is good
Pushbutton switch, when activated, for the defogger, seems to energise a relay and indicator light glows.
With 30A fuse removed, switch operates but no indicator light.

I suspect the relay control for this switch but have no clue how to get at it.

Any advice greatly appreciated!!

[DanD]

The "relay control" or timing circuit is incorporated in the Heater/AC control assembly and I don’t think it can be serviced separately.
You’ve already confirmed that the purple wire at the window doesn’t have power and that the fuses are good.
I would now go to the control assembly, pull it out of the dash leaving it connected electrically. Turn the ignition switch to the run position and confirm you have voltage and a good connection at the orange wire to the control.
If not chase the orange wire back to the fuse panel, (notice the splice # C204, splices like to burn open on the higher current flow circuits)
If there is power and the connection is good, turn the defroster switch on, to see if you have power leaving the control on the purple wire. If not the control has gone bad and you’ll have to replace the complete control assembly.
If there is power, you’re into a bit of search and rescue trying to finding the bad connection at one of the splices (C204&C220) or where the purple wire is broken.
It’s not hard work but it can be frustrating at times.
Dan.

[solcany]

Thanks for the great schematic!!!!!!

It looks as if the on indicator is lit, the relay contact, when closed, is at least supplying enough power for the indicator (not much ~~0.020mA @ 12Vdc). A good sign, except when the load is high >10A or so, the relay contacts, when corroded, act like a high value resistor and no current. I should see a voltage there even if the contacts are bad, but I don't. Looks like an open somewhere.

Any hints on how to get at this, without a major teardown of the dash???

Thanks again!

[DanD]

In this case I would use a test light connected to a known good ground to test for power, making sure you leave the circuit intact and back-probe the purple wire at the connector of the controller. If the test light doesn’t light when you push the button then it doesn’t really matter whether the “relay contacts” are corroded or the pull in coil of the relay is bad the heater, ac and defogger control assembly is more or less junk.
Again making sure that the orange wire has power and its connections are good.
The trim panel should just pop out of its retaining clips, If you say that really fast it sounds easy, but sometimes it feels like the trim panel is going to break before the clips release. After me saying that have a long close look for any hidden screws. The rest of the disassembly should be strait forward.
The thing you need for dash work is patients, patients, and more patients.
Dan.

[Solcany]

Thanks

Any pictures available? What I have seen to get at the back of the control requires a dash disassambly, even though the control is next to the radio.

[DanD]

[Solcany]

Thanks.

In my car, piece 3, is 1 large piece that extends up and to the left and trims the instrument cluster and also below the steering column. Item 2, the screws, are in the same relative position, though. This piece also trims the center and left air vents. The "purple" hot wire to the defroster is black, in my car. I understand the term is used "J car" for the Cavaliers. Any thought?

[Solcany]

This link and the pictures shows a closer representation of my situation. This is a "J Body"
www.j-body.org/library/howto.php?9

[DanD]

Yes I understand that a Cavalier is a J body car and those pictures you’ve posted look like they show everything you need to take it apart.
As for the Purple wire that’s what it shows on the diagram, it’ may turn into a black wire back at the window, due to the change between the dash wiring harness and the body harness. Let me know what you find on the actual control head.
Dan.

[Tom Greenleaf]

Quick thought - if and only if this car is a hatchback - look at where wires have to bend. T

[Solcany]

Its not a hatchback, thanks. I was able to get it all apart, thanks to the link above and verify that the wiring colours match the connectors on the above defogger control diagram.

Bottom line is the 12Vdc goes into the control and none comes out, even though the relay is pulling in. I would like to rip this apart, to have a go at it for a repair, any suggestions how to get inside the "sub module" for AC and Defogger?

It looks as if the entire panel will have to be replaced, if I cannot repair this section of the panel module. Any thoughts and advice?

Thanks and Happy Thanksgiving (Canadian)

[DanD]

There’s a local shop here that rebuilds these things so it is possible but finding any info on its internals seems like a well-hidden secret.
If you are going to try and open the control to have a look, be ready, the one I opened came apart in a big hurry as in pieces all over. All I wanted to do was replace the back-light bulbs, one half of the control was dark but they turned out to be a couple of LEDs, which were hard, soldered to the circuit board. Needless to say the control is back in my wife’s car, still dark. LOL
Thanksgiving, I can barely move from all the food but it’s always a good time, sitting with friends and family, stuffing your face. LOL
Thanks.
Dan.

[Solcany]

Replaced the control panel @ 60$. Got voltage at the defogger connector on back window. Connected wire and voltage dropped to 0. Burned contact/melted on connector plug wiring bundle from rear wiring to dash wiring, which was under the dash by left foot of driver. It has about 6 or so connections. Looks like the contact became resistive, generated heat and oxidized. Typical voltage/no current connection and all voltage dropped across the connector when loaded. Plan to splice this one wire with insulated crimp style push on connectors. Window element reads about 1 ohm so looks like at least 14 amps when motor is running.

Any suggestions for connector, male and female?

Thanks

[DanD]

I would solder the connections and insulate them with shrink tube.
The only reason there’s a connector there, is for assembly sake and it’s not like you’re going to need to disconnect it again.
Dan.

[Solcany]

All fixed, thanks!!

I noticed that the heater flow controls are still letting some air pass to the floor when vents are selected and vice versa. Any adjustments available or is this normal?