Rear Defrost help

[Tbruz]

Trouble shooting the rear defroster on my 1997 Tahoe with Barn doors.
I have measured 13.X volts at the posts on either side of the body so I know the switch and body wiring work; (drivers side is bottom pin, passenger side is top pin.) Zero volts with switch off, 13.x volts with switch on.
I have continuity thru the grid on each glass so I know there are no breaks to worry about and I have cleaned the contacts on the doors and the pins on the body with emery cloth and added Dielectric grease.
Measuring the defroster grid in the glass, Im only getting 4 volts thru this grid where I should be seeing 12 to 13 V.
What am I missing?

Thanks
Tbruz

 

[SunlitComet]

That the door jamb contact are probably already tosted to much that emery cloth may not help much. BTW on left door one pin is for power other is for ground return to body so both need to be intact. Same on right door two pins for window, next two down are power lock actuator module and bottom fifth is like a door jamb switch for interior lighting. I know dielectric grase is good in some places but if your have it filmed on the contacts it not like at plug where the terminals scrape each other to force a connection. A pin lands on a flat surface with no sideways movements it will probably for a thin insulating film between the two electrical points. In other words try it again with no dielectric grease on the contacts. I terminals check out like you said but lack when door closed they are no good anymore.

 

[Tbruz]

Thanks, I'll try replacing both the plunger side and the contact side of both doors.
Tony

 

[medic69]

Were you able to find some of the plungers? My 95 Tahoe is doing the same thing but I can not find the pins anywhere. Do you have a part number?

Thanks

Chet

 

[Tbruz]

Part numbers are 15693403 for the D/S and 15693402 for the P/S.
Both should be available at dealer or at GM parts direct.
cost was around $40.00 for both.
While I am able to measure a full 12+ volts at these pins; I have not seen a huge increase in voltage at the Defrost grid(thus not a huge change on defroster performance) after I changed these out.
No breaks in the defrost grid as proven by a continuity check.
Maybe I have a ground problem?
Looking for adviseon how to/where to test how good a ground is.
Tbruz

 

[SunlitComet]

ground should be right behind the those door jambs under neath the plastic trim somewhere in the body side. did you do the door side contact plates as well? I know I have to do all for pieces on mine soon.

 

[Tbruz]

Yup, replaced the contact side as well as the plunger side on both the Drivers and Passenger side(I have barn doors)
Voltage across the defroster grid doesn't measure 12+ volts.
Agian it does measure 12+ volts at the plunger with the doors open.
Any ideas on what I should check?
Could it be a weak ground wherever the ground plunger pin/contact actually connects to ground?
Thanks,
Tony

 

[SunlitComet]

the two top pins on either door are the power and ground contacts for grid. the right cargo door has three more. the next two down are for the door lock actuator. the bottom fifth pin does not carry current, it is a door ajar plunger similar to the side doors(in function anyway). Are you saying either door does not work at all?

Here is a not about the elements from alldata that might be helpful.

CHECK for a broken (or partially broken) wire inside of the insulation which could cause system malfunction but prove "GOOD" in a Continuity/Voltage check with a system disconnected. These Circuits may be intermittent or resistive when loaded, and if possible, should be checked by monitoring for a Voltage drop with the system operational (under load).

---------- Post added at 09:10 AM ---------- Previous post was at 09:08 AM ----------

How about the terminal behind the glass trim on the inside of the door?

 

[Tbruz]

Both left and right barn doors measure 12+ Volts on the truck side, the plunger side.
Closing the doors and measuring voltage on the defroster grid(The rear glass) I get much less voltage, around 4.5v to 7v per defroster line.
I measured a friends Tahoe and it has same voltage on glass as the plungers, 12+v.

A continuity check on the glass shows expected continous electrical path.

Your last post sounds like my issue; a resisistive load that is stopping some of the 12V from flowing thru to the grid/glass.
No sure what next steps should be; run a new clean wire from glass to door connector?
Is there a seperate cable form glass to door contacts or is it a part of the Glass?
I do know replacing glass is not in the cards.
Thanks,
Tony

 

[SunlitComet]

To cold out right now but will look tomorrow but I thought there was a block that attaches to the grid and a wire to it. It can be disconnected.


Pulled up the parts catalog. Ok I think the terminal block is bonded to glass. There is a seperate wire harness from door jamb contacts to window element block.

Were you getting the low voltage reading on the door side contacts, where it attaches to windows or downstream after going thru the grid?