[Richard]

The doors should NOT move freely in either direction.

The cylinder that moves the door is a double acting piston, meaning it needs pressure to move it in either direction. The electrical switch activates a pneumatic valve assembly that pressurizes the cylinder on one side to make it move in one direction, and when the switch is released that pressure should hold. Pressing the switch to move the door to the other side then pressurizes the opposite side of the piston AND releases the air that was originally holding the piston.

All of that background explanation to get to what is wrong.

In the simplest scenario the air line from the pneumatic valve to the cylinder is leaking.
The second scenario is the piston itself is leaking. If the door moves freely in either direction, a leaking piston is a likely culprit.
The third, and most likely scenario is the spool in the pneumatic actuator is worn out, allowing the air that is supposed to hold the door to leak out from the actuator. Tightening or adjusting the little brass exhaust valve regulators on the pneumatic valve is not the fix. Replacing the pneumatic actuator is the fix. You will have to get the number off it to order a new one. Newell used different ones in different years. When specing out a new one, it will be double acting center hold.