Power Window not working-1993 Mazda 626

One of the power windows of my 93 Mazda 626 stopped working. It is the front passenger window. Both switches at the driver side and at the passenger side were unable to make it work.

Troubleshooting

First of all, I operated the power window switch and listened if there was any sound of motor running. It is to identify if the problem is of electrical nature or or mechanical nature. (If there is sound of motor running, then the motor received power and implied that the electrical wiring is good. If there is not, then no conclusion can be drawn.) In my case, it was a dead silence. Then I monitor the battery voltage at the cigarette lighter plug while operating the power window switch. If the circuit draws current, the voltage will drop. In my case, there was no visible voltage drop.

At this point, I could conclude that there was an open circuit fault, maybe that the fuse was blown, or that the connector plug was loosen… I'm quite sure that it's not the switch as it would be a very low chance that both the passenger & driver side switches failed at the same time.

Then, I operated other windows. They worked fine. It eliminated the possibility of a blown fuse (I think that the windows share a single fuse but not 100% positive). The next thing that needed to do was to check power at the connector plug. It requires removal of the inner door panel. The inner door panel is secured by 2 clips at the upper edge, 2 screws close to the bottom and 7 plastic push pins around the panel perimeter. Remove the screws (one more screw needs to be removed, see the picture below) and pry the panel out with a pry bar or a 12” flat screw driver. 

Then lift the panel to unhook it from the upper edge. It should be off right away, (still with some electrical wiring hooking the panel).

Now, unplug the motor and check power at the feeding side while operating the power window switch. In my case, the 12V power presented (+12.4V and -12.4V respectively while toggling the switch). At that point, I could conclude that the motor has an open circuit fault.

I called a repair shop for a quote for replacing the motor. It turned out that the whole window regulator assembly needs to be replaced because the motor cannot be replaced on its own. The window regulator assembly costs $280 plus $100 labour plus tax. Total $425.

Oh my god! It is too much for me. I think I rather live with a dead window until I found a cheap one from wreck yard. For now, what I need to do is to find my way to close the window.

Having taking off the door panel, I decided to take the window regulator out to see if I can do anything. So I unplugged all connectors and store the panel in the trunk. Peeled off the moist barrier and remove the 3 bolts and 2 nuts which secured the window regulator.

Then I removed the 2 screws which secured the glass to the window regulator. (See the pictures below). 

Once the glass is free, push it all the way up and duct tape it to the door. Then the window regulator can be taken out through the biggest opening.

The window regulator is shown below.

Tested the motor on bench and confirmed that it was open circuit. I removed the motor enclosure and found that the commutator of the motor has been very dirty. I cleaned the commutator with paint thinner and a tooth brush until the copper shown up. 

These pictures were taken after the commutator was cleaned.

Put the armature back and tested the motor with bench power supply.

It worked! I saved $425?! No, it was too early to jump to the end.  It only ran on no load. It barely ran after it was reinstalled to the door. It needed to be assisted with manual push on the glass to close the window. It was because the carbon brush and the commutator of the motor have been worn out. They do not make a good contact even they were cleaned. I still need to hunt for a cheap replacement, just live with it for now.

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End of the project

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