When a window regulator or regulator motor fails it is almost never in the summer. Seems to happen to me only in winter when weather is severe! Getting the window up and then keeping it up tight may be necessary until you can repair it or get the replacement parts. Tape and other "quick fixes" don't work for me. The window always works itself down and then you get loud wind noise.
Problem & Solution
Common among these chassis:
Here is the method I have used successfully over the past few years. It requires a length of 2 x 2 wood and a chunk of white packing foam. Remove the regulator and push the window all the way up. Tape it to hold in place temporarily. Put the chunk of foam in the bottom of the door and then measure from top of foam to bottom of window. Cut the 2 x 2 about 1/2 to 3/4 inches longer than your measurement. That way you can JAM the wood in on top the foam and it will compress to hold firmly in place. For some this may become a permanent repair.... :-)
If you have a 126 chassis it may just be an easy fix by installing a new plastic slide. Other models usually require replacement of regulator or motor.