crap Forget what I said. I was mixed up, guys
For some reason I thought we were talking about locks and not windows. (that's why I said solenoid.) Sorry.

I think those windows use thermal cutouts. So when the motor stalls, there's a part that heats up, maybe a bimetallic strip.

Anyway, it could be the motor, but I wouldn't rule out other causes. There's a lifting mechanism, probably with some plastic parts. The lube eventually dries out and might be seized. A gear might have skipped a tooth etc.
The motor is likely an ordinary DC variety. The brushes eventually wear out. Either way, it seems like you need to disassemble the door.

 

Thanks guys. I have a crazy schedule for the next few days. I'll get back at it this weekend and let you know how it goes.

 

i own an autoglass company and have fixed many of these.....the best way to check the motor is to remove the door panel and jump the motor directly.....the motor will work or it dosent....it doesnt really know up or down....next check the switches.....the switches are in series so if one goes out it wont work from either side check to see if there is power at the switches....then .....this is the big one....the wires that exit the door through the rubber boot get broken with time.....ive seen this over and over....the constant open and closing the door fatigues the wires and they break...some times without breaking the insulation......

 

you can also change the motor without removing the regulator.....removing the regulator is a pain in the a$$

 

How do you separate the motor from the regulator? Does it just slip off? The Haynes manual says to avoid personal injury the tension from the counter balance spring needs to be relieved by screwing a sheet metal screw into a hole to lock the sector gear. I don't see a similar warning in the Clymer manual.

Sorry guys if I seem a little dense here. I find the direction given by the Clymer manual and the Hanes manual I have are pretty vague on the details. I'm just a shade tree mechanic but I have completely rebuilt a Datsun 510 engine and replaced a synchro in VW Vanagon but I'm finding this silly regulator motor replacement to be pretty mysterious and frustrating.

 

OK, as usual I got it figured out after venting some frustration.

After a little more investigating I found that there are three bolts that fasten the motor to the regulator. It turns out that two of the bolts holding the motor are covered by sheet metal and the third was partially covered. Looks like Chevy's intent was to require both the motor and regulator to be taken out for servicing. I took my dremel and made openings to remove the bolts and was able to remove the motor. The motor does not turn when connected directly to 12V so I'll get one ordered pronto.

Here's a picture showing the three access holes that were made:



Thanks all for the assistance. I'll follow up after I get the replacement motor installed.

 

Late to the party as always, good to see you figured something out. My '93 replacement motor had the regulator attached and the swap was just tape window in place, 3 bolts out, motor/regulator combo out, reverse. As always, compare old to new and test when possible (I waited to test until I had everything in place loosely so regulator wouldn't be out of place before installation).

 

i use a bi metal hole saw to access the obstructed rivets holding the motor to the regulator ....leave the glass in place when you do this.....it will keep the regulator in place and keep tension on the regulator spring......if you decide to remove the regulator and motor together remove the spring with a vice grip first before you remove the motor.....watch your fingers...the spring is under a lot of tension......when you purchase the new motor it should come with small screws to use in place of the rivets....i like to use 3/16 rivets but you will need to drill the regulator and corresponding holes in the motor.......the motor is called a pancake motor and they are notorious for failing......and all around the motor are mounting holes for different applications...make sure you match the new motor to the old one to see what holes you want to modify to 3/16 ( or use the little screws )...also check the teeth count on the motors to make sure they are the same. different applications use different teeth count