2000 Chrysler LHS Rear Defroster

Tiny
TAZMANSHADOW
  • MEMBER
  • 2000 CHRYSLER LHS
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 139,000 MILES
My first problem was the ATC head display wouldn't stay on so I replaced the head with one that did and is suppose to be compatible. The only diffrence between the two is my original one had led lights showing the front and back defrost was on and rear defrost was not displayed on head. The one I put in doesn't have them. The problem is that when I first got the car the rear def. Worked but since I replaced the ATC heads it doesn't. The side mirrors defrost but not the back window. I checked for continuity between the two sides of the window and it has it. I plugged in the old ATC head just to see if the def. Would work but it doesn't. I can't find a fuse in the owner's manual that controls the defroster and like I said the side mirrors do defrost which is part of the same circuit from my understanding. I don't know how to check for power going through or to the window grid. I was appreciate any help you could give me.
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Thursday, November 12th, 2009 AT 7:50 AM

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Tiny
CARADIODOC
  • EXPERT
Nice to see a post with lots of information and preliminary diagnosis. Thank you.

According to the service manual, if you have memory seats / mirrors, the heated mirrors and the rear window heater are on the same circuit. If you do NOT have memory seats, there is a radio antenna module in the circuit going to the rear heater. I'm not familiar with that unit.

I can't see anything that would cause your problem related to replacing the controller. Since the mirrors are working, use a cheap test light, (not an expensive voltmeter), to check for voltage on the two terminals on the sides of the rear window. A voltmeter doesn't cause any current to flow in the circuit so it could give false readings in this type of circuit.

If you find 0 volts on both terminals, you'll need to find that antenna module or follow the wire back to a break or a corroded splice. If you find 12 volts on both terminals, the ground is open. Look for a terminal broken off the window glass, or the wire is loose where it bolts to the body. (Is it possible the rear heater quit working before you replaced the controller, but you just didn't notice it until now, because that would be two unrelated problems)?

If you find the proper 12 volts on one side and 0 volts on the other side, the system is working properly, but if the glass isn't getting warm, the grid lines are open, possibly from kids scratching them or from aggressive cleaning. Touch the test light to the center of each grid line, or you can use a voltmeter here. In the center of the window, the test light should light up half brightness or the voltmeter should read around 6 volts. If you find 12 volts, the grid is open between that point and the grounded side. If you find 0 volts, the grid line is open between that point and the 12 volt supply side. You can find the break by moving the test light or meter probe along the grid line until the voltage changes. Every grid line must be tested the same way. One open line will not affect the operation of the others. If you do find some breaks, there is a kit available with paint that has copper powder in it to bridge the gaps. If you use it, don't feel the urge to test it for at least a day to be sure it has cured. I did that once, and it went up in smoke! The bottle of repair liquid is very small. I think you will find it at one of the auto parts stores. There is also an epoxy material with copper in it for gluing the terminals back onto the glass if one is broken off. I tried that three times on two different cars and had no success. There was too much pressure from the thick wires and the terminals kept breaking off.

One final note; the mirrors are protected by a 10 amp fuse after the relay, and the mirrors AND rear heater are protected by a 50 amp fuse under the hood before the relay. Both of them must be good since the mirrors are heating up. From what I can see in the service manual, since the mirrors are working, everything in the system is working properly with the exception of the feed wire to the rear glass, the glass itself, or the ground wire. Sorry I can't help you if it looks like there's a problem with the antenna module. I've never replaced one, never tested one, I don't even know what it looks like or where it lives.

Caradiodoc
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Sunday, November 29th, 2009 AT 2:03 AM

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