The rear windows in my '86 300E often won't work in the winter. Sometimes when the car is just idling they won't open but, at highway speeds when the alternator may be putting out a slightly higher voltage, the windows start working. I've also had a window, which wasn't opening, start to work when the sun warmed up that side of the car.

My theory is that the mechanism lubrication has hardened with age requiring more power from the battery and/or softening from heat. Note that my windows seem to work better in the summer.

Also sometimes in the rainy season I think deposits of ??? get washed into the seams between the window glass and the rubber around the windows. I've had windows suddenly open with a snapping sound when they haven't been opened for a long time. A spray of silicone lube in the window channels seems to help for this.

Next summer I plan to learn to take off the door panels. Then I'll clean and relube as many moving parts as I can find.

I've also had a mechanic tell me that it is a good idea to "exercise" each window regularly to keep the window moving freely.

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1986 300E
1993 Volvo 940 Wagon
1984 Volvo 240 (daughter's)
1976 Dodge 1/2T pickup, gas hog